Method for producing organic acid

ABSTRACT

A novel method is provided whereby a free organic acid can be produced particularly from an ammonium salt of an organic acid having a high melting point obtainable by bioconversion of a carbon source in the presence of a neutralizing agent, efficiently at a low cost, and the used material for reaction and a byproduct can be recycled for reuse without being disposed. 
     An ammonium salt of organic acid A such as a dicarboxylic acid, a tricarboxylic acid or an amino acid is subjected to reactive crystallization by means of acid B such as a monocarboxylic acid satisfying the following formula (1), to separate free organic acid A in solid form: 
         pKa ( A )≦ pKa ( B )  (1) 
     where pKa(A) and pKa(B) represent ionization indices of organic acid A and acid B, respectively, provided that when they have plural values, they represent the minimum pKa among them. 
     The crystallization mother liquor after precipitating and separating organic acid A is, after separating acid B and then an ammonium salt of acid B, recycled for use in the reactive crystallization step. The ammonium salt of acid B is decomposed into acid B and ammonia, which are recycled for use in the reactive crystallization step and as a neutralizing agent in the bioconversion step, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/688,647, filed on Mar. 20, 2007, which is a divisional ofU.S. patent application Ser. No. 10/976,822, filed on Nov. 1, 2004,which is a continuation of International patent applicationPCT/JP03/05826, filed on May 9, 2003, which claims priority to Japanesepatent application JP 2002-305989, filed on Oct. 21, 2002, Japanesepatent application JP 2002-231741, filed on Aug. 8, 2002, Japanesepatent application JP 2002-231740, filed on Aug. 8, 2002, and Japanesepatent application JP 2002-135656, filed on May 10, 2002, the contentsof which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to method for producing an organic acidhaving a high melting point such as a dicarboxylic acid, a tricarboxylicacid or an amino acid (hereinafter sometimes generally referred to asorganic acid A). More particularly, it relates to a method for producingan organic acid comprising a novel separation/purification step of anorganic acid, which is useful in a case where a biogenic material suchas glucose, fructose or cellulose, is produced by bioconversion.

BACKGROUND ART

A carboxylic acid such as succinic acid or its derivative is widely usedas a material for a polymer such as a polyester or a polyamide,particularly as a material for a biodegradable polyester, or as amaterial for food products, pharmaceuticals and cosmetics. Further, atricarboxylic acid such as citric acid is widely used as a foodadditive, etc. In recent years, particularly succinic acid is expectedto be a material for a biodegradable polymer, together with lactic acid.

Succinic acid has heretofore been industrially obtained by hydrogenationof maleic acid, and the maleic acid is a material derived frompetroleum. Accordingly, as a technique to produce an organic acid suchas succinic acid, malic acid, tartaric acid or citric acid from amaterial derived from a plant, a technique to utilize a fermentationoperation has been studied. Further, an amino acid has already beenproduced by a fermentation method, but separation and purification of anamino acid have been carried out usually by isoelectric pointprecipitation employing sulfuric acid.

Further, such an organic acid as a dicarboxylic acid or a tricarboxylicacid has at least two carboxyl groups, or carboxyl groups and an aminogroup, as functional groups. Due to such hydrogen bonds, its meltingpoint is usually high (usually at least 120° C.), and in its productionprocess, a distillation operation as a common separation/purificationmethod, can not be employed. Further, in the production of such anorganic acid by fermentation, neutralization is usually required, sincea microorganism such as fungus or mold to be used for the fermentationdoes not show an adequate activity usually under a low pH condition.Accordingly, an organic acid obtainable from a fermenter, is usually inthe form of a salt with an alkali used for the neutralization. This is afactor which makes the separation/purification of such an organic acidmore difficult.

Heretofore, a method employing electrodialysis (JP-A-2-283289) isavailable as a common separation/purification method for a salt of anorganic acid formed by fermentation. However, the electrodialysis has aproblem that since the apparatus is large in proportion to productionscale, and the scale merit is small even by production on an industrialscale, and consequently the cost tends to be high.

Further, a method of employing an ion exchange resin has been proposed(U.S. Pat. No. 6,284,904). However, in this method, a salt of a strongacid and strong base (such as NaCl) will be formed at the time ofregenerating the ion exchange resin, and eventually, this salt isrequired to be disposed or to be treated by electrodialysis.

Further, a method of decomposing calcium succinate with sulfuric acidhas been proposed (JP-A-3-030685). However, in this method, calciumsulfate will be formed in a large amount as a byproduct, and itstreatment is problematic.

Further, as an effective method, a method of carrying out reactivecrystallization by an exchange reaction of a salt by means of sulfuricacid has been proposed (JP-A-2001-514900, U.S. Pat. No. 5,958,744).Namely, this is a method for precipitating and separating an organicacid by carrying out reactive crystallization by adding sulfuric acid toan ammonium salt of an organic acid.

In this method, a soluble amount of the ammonium salt of the organicacid will remain in the crystallization mother liquor after separatingthe organic acid by crystallization, and ammonium sulfate will also becontained in this crystallization mother liquor. In order to increasethe recovery rate of the entire process, it is necessary to recover suchan ammonium salt of the organic acid remaining in the crystallizationmother liquor, but even if a crystallization operation is furtherapplied to this crystallization mother liquor, it is extremely difficultto separate ammonium sulfate in solid form, while permitting theammonium salt of the organic acid to remain in the liquid. Otherwise,even if it is attempted to carry out separation by a gas/liquidseparation operation such as distillation, the ammonium salt of theorganic acid and ammonium sulfate have very high melting points, andunder such a high temperature condition as to vaporize these compounds,the ammonium salt of the organic acid will undergo a dehydrationreaction, and it would be impossible to recover the organic acid.Further, by this method, a special installation has been required tocarry out pyrolysis of ammonium sulfate at a temperature of at least300° C. in order to recover and reuse sulfuric acid from ammoniumsulfate.

It is an object of the present invention to solve such conventionalproblems and to provide a novel method for producing organic acid Ahaving a high purity by separating and purifying free organic acid Afrom a salt of organic acid A formed by a fermentation method bybioconversion of a carbon source in the presence of a neutralizingagent.

Another object of the present invention is to provide a method forproducing organic acid A efficiently at a low cost with a low level ofwaste in consideration of environment, by decomposing and reusing abyproduct salt formed in the above-mentioned novel method for producingorganic acid A.

DISCLOSURE OF THE INVENTION

As a result of an extensive research on the above problems, the presentinventor has paid particular attention to characteristics of organicacid A to be obtained in the present invention such that its solubilityin a monocarboxylic acid (hereinafter sometimes referred to as acid B)being a weak acid such as acetic acid or propionic acid, is generallylow and its temperature dependency is high, and an ammonium salt oforganic acid A has a high solubility in acid B. It has been found thatby utilizing such characteristics, it is possible to separate theammonium salt of organic acid A which should be hardly decomposable whenjudged solely from pKa (Ka: dissociation constant, pKa=log₁₀Ka), in theform of an acid, by reactive crystallization by means of acid B, and itis possible to decompose an ammonium salt of acid B formed as abyproduct, under a relatively mild heating condition, and it is possibleto reuse ammonia obtained by the decomposition.

In the present invention, “an ammonium salt” means a mono-, di- and/ortri-ammonium salt, unless otherwise defined.

It is a well known fact that in general, a salt of a weak acid can bedecomposed by a strong acid by means of an exchange reaction of the saltto produce a salt of the strong acid as a byproduct and to obtain theweak acid. This is the above-mentioned conventional method for carryingout an exchange reaction of a salt by means of sulfuric acid (U.S. Pat.No. 5,958,744). Further, also in the method of employing an ion exchangeresin, the ion exchange resin is required to be an acid stronger than adicarboxylic acid or a tricarboxylic acid. However, as mentioned above,in such a method, a salt of an acid stronger than the desired organicacid will be formed as a byproduct.

When comparison is made with respect to pKa as an index for the acidintensity in an acid/base exchange reaction, for example, pKa ofsuccinic acid and acetic acid is as shown below, and it is evident thatdiammonium succinate (secondary kPa) is capable of an acid/base exchangereaction with acetic acid, but monoammonium succinate is hardly capableof such an acid/base exchange reaction with acetic acid.

Succinic acid primary pKa: 4.21

Succinic acid secondary pKa: 5.64

Acetic acid pKa: 4.76

Accordingly, as mentioned above, it has been common to employ a methodof using a strong acid or an ion exchange resin having a strong acidity.As shown in JP-A-2001-514900, in the crystallization employing aninorganic acid, it is usually required to have a high recovery rate by asingle stage of crystallization, since an ammonium salt of the inorganicacid is usually non-volatile. Accordingly, in the case of succinic acid,primary pKa is 4.21, whereby the pH must be smaller than 2.1 in order toobtain a sufficient recovery rate. Thus, in JP-A-2001-514900, sulfuricacid is used for the reactive crystallization. In this method, the pH isrequired to be from 1.5 to 1.8.

Whereas, the present inventor has discovered that organic acid A whichis difficult to obtain solely by an acid/base reaction, can be easilyseparated and purified by reactive crystallization by means of acid Bsuch as a monocarboxylic acid, which is an acid weaker than the desiredorganic acid A.

Namely, paying an attention to the fact that organic acid A obtainableas a result of bioconversion in the presence of a neutralizing agent,has a high solubility as an ammonium salt of organic acid A and a lowsolubility as ammonia free organic acid A, in acid B as a weak acid, thepresent inventor has found a fact that there is a region wherein it issoluble as an ammonium salt of organic acid A, but insoluble as ammoniafree organic acid A, in acid B.

On the other hand, acid B functions as a proton source, whereby bypermitting a sufficient amount of acid B to be coexistent, to lower thepH, it is possible to convert the ammonium salt of organic acid A toammonia free organic acid A by an acid/base reaction with acid B. Ifsuch ammonia free organic acid A is present beyond the solubility, theammonia free organic acid A precipitates. At that time organic acid A inthe form of ammonium salt has a sufficiently high solubility in acid Band will not precipitate at the same time.

On the basis of such discoveries, the present inventor has succeeded inseparating organic acid A which used to be difficult to obtain solely byan acid/base reaction, in solid form, by reactive crystallization bymeans of acid B which is a weaker acid than organic acid A.

On the other hand, in such a case, there may be a case where therecovery per stage tends to be poor as compared with conventionalcrystallization employing a strong acid. Therefore, it is preferred thatthe ammonium salt of acid B formed as a byproduct and the ammonium saltof organic acid A, contained in the mother liquor, are separated andrecovered from the mother liquor and recycled, for industrial operation.Further, if the salt of acid B formed as a byproduct, is disposed, aproblem of a disposed waste will be created like the conventionaltechnique, and accordingly, it is preferred to decompose and reuse theammonium salt of acid B formed as a byproduct.

The present inventor has found that ammonia constituting the ammoniumsalt of organic acid A is a volatile base, and in a case where avolatile acid, preferably a saturated monocarboxylic acid having a lowboiling point such as acetic acid or propionic acid is used as acid B,it is possible to vaporize the ammonium salt of acid B. By thisoperation, they have succeeded in recovering organic acid A from themother liquor obtained by reactive crystallization.

Thus, the present invention is characterized by having the followingfeatures.

1. A method for producing organic acid A, which comprises subjecting anammonium salt of organic acid A to reactive crystallization by means ofacid B satisfying the following formula (1), to separate organic acid Ain solid form:

pKa(A)≦pKa(B)  (1)

where pKa(A) and pKa(B) represent ionization indices of organic acid Aand acid B, respectively, provided that when they have plural values,they represent the minimum pKa among them.2. The method according to Item 1, wherein acid B is volatile.3. The method according to Item 1 or 2, wherein organic acid A is anorganic acid having a melting point of at least 120° C.4. The method according to Item 1 or 2, wherein organic acid A is aC₄₋₁₂ dicarboxylic or tricarboxylic acid, or a C₄₋₁₂ amino acid.5. The method according to any one of Items 1 to 4, wherein acid B is amonocarboxylic acid.6. The method according to any one of Items 1 to 4, wherein acid B isacetic acid or propionic acid.7. The method according to any one of Items 1 to 6, wherein the reactivecrystallization is carried out in a single stage or multi-stages, andthe pH is from 2.1 to 6.5 at least in one stage.8. The method according to any one of Items 1 to 7, wherein the ammoniumsalt of organic acid A is one obtained via a bioconversion step in whicha carbon source is converted by a microorganism in the presence of atleast one neutralizing agent selected from the group consisting ofammonia, ammonium carbonate and urea.9. The method according to any one of Items 1 to 7, wherein the ammoniumsalt of organic acid A is one obtained in the form of an aqueoussolution of the ammonium salt of organic acid A in such a manner that areaction solution containing an alkali metal and/or alkaline earth metalsalt of organic acid A is obtained via a bioconversion step in which acarbon source is converted by a microorganism in the presence of atleast one neutralizing agent selected from the group consisting of analkali metal hydroxide, an alkaline earth metal hydroxide, an alkalimetal carbonate and an alkaline earth metal carbonate; ammonia andcarbon dioxide, and/or ammonium carbonate, is added to said reactionsolution containing an alkali metal and/or alkaline earth metal salt oforganic acid A to carry out reactive crystallization to precipitate analkali metal and/or alkaline earth metal carbonate (Solvay processstep); and the precipitated carbonate is separated.10. The method according to Item 8 or 9, which includes a concentrationstep of concentrating the reaction solution obtained in thebioconversion step, and wherein a concentrate obtained in theconcentration step is subjected to the reactive crystallization.11. The method according to any one of Items 1 to 7, wherein theammonium salt of organic acid A is one formed in a chemical process.12. The method according to any one of Items 1 to 11, wherein organicacid A precipitated by the reactive crystallization is separated; afterthe separation, an ammonium salt of acid B in the crystallization motherliquor is decomposed by a decomposition step to obtain acid B; and theobtained acid B is recycled for use as a solvent for the reactivecrystallization.13. The method according to Item 12, wherein organic acid A precipitatedby the reactive crystallization is separated; after the separation, thecrystallization mother liquor is concentrated by vaporizing acid Btherefrom; and then, the acid B and its ammonium salt aredecomposed/vaporized in order to recover organic acid A and its ammoniumsalt.14. The method according to Item 13, wherein the vaporization of acid Bis carried out at a temperature of not higher than the melting point ofthe ammonium salt of acid B.15. The method according to Item 13 or 14, wherein thedecomposition/vaporization of the acid B and its ammonium salt arecarried out by heating under a reduced pressure of from 0.001 mmHg to200 mmHg.16. The method according to any one of Items 12 to 15, wherein thedecomposition step comprises a heating step of heating a liquidcomprising the ammonium salt of acid B, an alkali metal and/or alkalineearth metal salt of acid B, and water, and withdrawing a gas of a basicaqueous solution, and a step of subjecting the basic aqueous solutionwithdrawn from the heating step, directly or after condensation, togas/liquid separation, gas/solid separation or gas/liquid/solidseparation at a temperature of not higher than the melting point of theammonium salt of acid B.17. The method according to any one of Items 12 to 15, wherein thedecomposition step comprises a heating step of supplying a liquidcomprising the ammonium salt of acid B, an alkali metal and/or alkalineearth metal salt of acid B, and water, to a distillation column havingat least two plates as the real number of plates, and withdrawing a gasof a basic aqueous solution from the top of the distillation column.18. The method according to Item 17, wherein in the heating step, theliquid comprising the ammonium salt of acid B, an alkali metal and/oralkaline earth metal salt of acid B, and water, is supplied to a site ofthe distillation column having at least two plates as the real number ofplates, where the temperature is not higher than the melting point ofthe ammonium salt of acid B.19. The method according to any one of Items 16 to 18, wherein thealkali metal and/or alkaline earth metal constituting the alkali metaland/or alkaline earth metal salt of acid B, is at least one memberselected from the group consisting of Na, K, Ca and Mg.20. The method according to any one of Items 16 to 18, wherein theliquid after withdrawing the gas of a basic aqueous solution in theheating step, is subjected to a separation step which is carried outunder reduced pressure or atmospheric pressure at a temperature of atleast 125° C., to separate and recover acid B.21. The method according to Item 20, wherein the residual liquid afterthe separation step is mixed with a system containing water to hydrolyzean amide compound formed as a byproduct in the heating step and theseparation step and then recycled to the heating step.22. The method according to any one of Items 1 to 10 and 12 to 21,wherein the ammonium salt of organic acid A is one obtained as areaction solution containing the ammonium salt of organic acid A via abioconversion step in which conversion is carried out by a microorganismby means of ammonia as a neutralizing agent; organic acid A precipitatedby the reactive crystallization carried out by adding acid B, isseparated; after the separation, the ammonium salt of acid B in thecrystallization mother liquor, is decomposed to obtain ammonia; and theammonia is used as a neutralizing agent for the bioconversion step.23. The method according to any one of Items 1 to 10 and 12 to 21,wherein the ammonium salt of organic acid A is one obtained in the formof an aqueous solution of the ammonium salt of organic acid A in such amanner that a reaction solution containing an alkali metal and/oralkaline earth metal salt of organic acid A is obtained via abioconversion step in which a carbon source is converted by amicroorganism in the presence of at least one neutralizing agentselected from the group consisting of an alkali metal hydroxide, analkaline earth metal hydroxide, an alkali metal carbonate and analkaline earth metal carbonate; ammonia and carbon dioxide, and/orammonium carbonate, is added to said reaction solution containing analkali metal and/or alkaline earth metal salt of organic acid A to carryout reactive crystallization to precipitate an alkali metal and/oralkaline earth metal carbonate (Solvay process step); and theprecipitated carbonate is separated; organic acid A precipitated by thereactive crystallization carried out by adding acid B, is separated;after the separation, the ammonium salt of acid B in the crystallizationmother liquor, is decomposed to obtain ammonia; and the ammonia is usedas an ammonia source for the Solvay process step.24. The method according to any one of Items 1 to 23, wherein thereactive crystallization is carried out in multi-stages, and in reactivecrystallization in the second or subsequent stage, the crystallizationmother liquor after separating the precipitated organic acid A is,directly or after concentrating the ammonium salt of acid B byvaporization of the reactive crystallization solvent containing acid B,or after separating organic acid A or its salt dissolved in the motherliquor, recycled to a crystallizer for reactive crystallization in apreceding stage.25. In a process for separating and recovering acid B and ammonia bydecomposing an ammonium salt of acid B to acid B and ammonia, a methodfor decomposing the ammonium salt of acid B, which comprises a heatingstep of heating a liquid comprising the ammonium salt of acid B, analkali metal and/or alkaline earth metal salt of acid B, and water, andwithdrawing a gas of a basic aqueous solution, and a step of subjectingthe basic aqueous solution withdrawn from the heating step, directly orafter condensation, to gas/liquid separation, gas/solid separation orgas/liquid/solid separation at a temperature of not higher than themelting point of the ammonium salt of acid B.26. In a process for separating and recovering acid B and ammonia bydecomposing an ammonium salt of acid B to acid B and ammonia, a methodfor decomposing the ammonium salt of acid B, which comprises a heatingstep of supplying a liquid comprising the ammonium salt of acid B, analkali metal and/or alkaline earth metal salt of acid B, and water, to asite of a distillation column having at least two plates as the realnumber of plates, where the temperature is not higher than the meltingpoint of the ammonium salt of acid B, and withdrawing a gas of a basicaqueous solution from the top of the distillation column.27. The method according to Item 25 or 26, wherein the alkali metaland/or alkaline earth metal constituting the alkali metal and/oralkaline earth metal salt of acid B, is at least one member selectedfrom the group consisting of Na, K, Ca and Mg.28. The method according to any one of Items 25 to 27, wherein acid B isat least one member selected from the group consisting of formic acid,acetic acid, propionic acid and butyric acid.29. The method according to any one of Items 25 to 28, which comprises astep of recovering acid B, wherein the liquid after withdrawing the gasof a basic aqueous solution in the heating step, is subjected to aseparation step which is carried out under reduced pressure oratmospheric pressure at a temperature of at least 125° C., to separateand recover acid B.30. The method according to any one of Items 25 to 29, wherein theresidual liquid after the separation step is mixed with a systemcontaining water to hydrolyze an amide compound formed as a byproduct inthe heating step and the separation step and then recycled to theheating step.31. Organic acid A produced by a method as defined in any one of Items 1to 24.32. A polymer prepared by using, as a material, organic acid A producedby a method as defined in any one of Items 1 to 24.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flowchart showing the construction of an apparatussuitable for carrying out the method for decomposition of an ammoniumsalt of acid B of the present invention.

FIG. 2 is a schematic flowchart showing the construction of anotherapparatus suitable for carrying out the method for decomposition of anammonium salt of acid B of the present invention.

FIG. 3 is a schematic flowchart showing the construction of anotherapparatus suitable for carrying out the method for decomposition of anammonium salt of acid B of the present invention.

FIG. 4 is a schematic flowchart showing the construction of anotherapparatus suitable for carrying out the method for decomposition of anammonium salt of acid B of the present invention.

FIG. 5 is a schematic flowchart showing the construction of anotherapparatus suitable for carrying out the method for decomposition of anammonium salt of acid B of the present invention.

FIG. 6 is a flowchart showing the construction of the apparatus employedin Test Examples 2-2 and 2-3.

MEANING OF SYMBOLS

-   -   1, 1A, 1B: Distillation columns    -   2: Vaporizer    -   3: Acetamide decomposition vessel    -   4: Thin film evaporator    -   5: Flash drum    -   10: Distillation column    -   12: Oil bath    -   13: Flask    -   16: Feed material vessel    -   17: Preheater

EMBODIMENTS OF THE INVENTION

Now, embodiments of the method for producing an organic acid accordingto the present invention, will be described in detail.

Formation of an Ammonium Salt of Organic Acid A

Organic acid A to be produced by the present invention may, for example,be one having a melting point which is preferably at least 120° C. Itscarbon number is preferably from 4 to 12, and it is preferably onehaving a straight chain form. A dicarboxylic acid or a tricarboxylicacid may, for example, be mentioned as a typical example. Preferred isone having two or three carboxyl groups bonded to a saturated orunsaturated aliphatic hydrocarbon, and it may have a branched chain orcyclic structure, and it may have a substituent. Further, organic acid Aincludes an amino acid having a melting point which is preferably atleast 120° C.

Specifically, organic acid A may, for example, be succinic acid, fumaricacid, maleic acid, malic acid, tartaric acid, asparaginic acid, glutaricacid, glutamic acid, adipic acid, suberic acid, citric acid, itaconicacid, terephthalic acid, phenylalanine, tryptophan, asparagine,glutamine, valine, isoleucine, leucine, histidine, methionine ortyrosine. These acids may be a mixture of two or more of them. Amongthem, preferred as organic acid A is, for example, succinic acid, adipicacid, glutamic acid, suberic acid, tartaric acid or citric acid.Particularly preferred is succinic acid, adipic acid, glutamic acid orsuberic acid. Such organic acid A may be formed, for example, bybioconversion using a carbon source as the starting material. As thecarbon source, a fermentable carbohydrate, such as a carbohydrate suchas galactose, lactose, glucose, fructose, glycerol, sucrose, saccharose,starch or cellulose, or a polyalcohol such as glycerine, mannitol,xylitol or ribitol, may, for example, be used. Among them, glucose,fructose or glycerol is preferred. Particularly preferred is glucose. Asa broader plant-derived material, cellulose as the main component forpaper, is preferred. Further, a starch-succharized liquid or treaclecontaining the above-mentioned fermentable carbohydrate, may also beused. Such fermentable carbohydrates may be used alone or in combinationas a mixture of two or more of them.

The microorganism to be used for such bioconversion is not particularlylimited so long as it has an ability to produce organic acid A. Forexample, anaerobic bacteria such as genus Anaerobiospirillum (U.S. Pat.No. 5,143,833), facultative anaerobic bacteria such as genusActinobacillus (U.S. Pat. No. 5,504,004) or genus Escherichia (U.S. Pat.No. 5,770,435), or aerobic bacteria such as genus Corynebacterium (JP11113588) may, for example, be used. The reaction conditions such as thereaction temperature, pressure, etc., in the bioconversion, depend uponthe activities of the fungus, mold, etc. to be selected, but suitableconditions to obtain the corresponding organic acid A may be suitablyselected depending upon the respective cases.

In the above bioconversion, if the pH becomes low, the metabolicactivities of the microorganism tend to be low, or the microorganismtends to stop its activities, whereby the production yield is likely todeteriorate, or the microorganism is likely to die. Therefore, aneutralizing agent is used. Usually, the pH in the reaction system ismeasured by a pH sensor, and the pH is adjusted to be within aprescribed pH range, every time when a neutralizing agent is added. Inthe present invention, the method for adding a neutralizing agent is notparticularly limited, and it may be continuous addition or intermittentaddition.

The neutralizing agent may, for example, be ammonia, ammonium carbonate,urea, an alkali metal hydroxide, an alkaline earth metal hydroxide, analkali metal carbonate or an alkaline earth metal carbonate. Preferredis ammonia, ammonium carbonate or urea. Namely, as mentioned above, in acase where an alkali metal or alkaline earth metal hydroxide or analkali metal or an alkaline earth metal carbonate is employed, an alkalimetal or alkaline earth metal salt of acid B will be formed as abyproduct in the reactive crystallization by means of acid B, and thealkali metal or alkaline earth metal used for neutralization can notdirectly be recovered. Accordingly, in the Solvay process step, a stepof obtaining an ammonia salt of organic acid A will be required.Further, the alkali metal or alkaline earth metal hydroxide may, forexample, be NaOH, KOH, Ca(OH)₂, Mg(OH)₂, or a mixture thereof. Thealkali metal or alkaline earth metal carbonate may, for example, beNa₂CO₃, K₂CO₃, CaCO₃, MgCO₃, NaKCO₃ or a mixture thereof.

The pH value to be adjusted by such a neutralizing agent, is adjusteddepending upon the type of the fungus or mold to be used, within a rangewhere its activities are most effectively obtained. Usually, the pH iswithin a range of from 4 to 10, preferably from 6 to 9.

The ammonium salt of organic acid A to be the starting material fororganic acid A to be produced by the present invention, is notnecessarily limited to one obtained by the above-mentionedbioconversion, but may be one produced or produced as a byproduct from apetrochemical process or from other various processes.

Reactive Crystallization

In general, crystallization refers to an operation to precipitate thenecessary component in a state where unnecessary components aredissolved in a solvent. Whereas, in the present invention, “reactivecrystallization” means an operation whereby a necessary component isobtained by a reaction and at the same time crystallization is carriedout. Namely, it is meant for an operation in which crystallization ofthe desired product is carried out while carrying out a reaction toobtain the desired product to be crystallized. In the present invention,separation and purification of such organic acid A is carried out byreactive crystallization employing acid B which is a weaker acid thanorganic acid A, as mentioned above. Acid B to be used, is required tosatisfy the following formula (1):

pKa(A)≦pKa(B)  (1)

Here, in the formula (1), Ka(A) and Ka(B) represent the dissociationconstants of organic acid A and acid B, respectively, and in a casewhere they have plural values, they represent the minimum pKa amongthem. Although it may depend substantially on the functional groups oforganic acid A, pKa(B) is preferably larger by from 0 to 3 than pKa(A)while satisfying the above formula (1).

As an example of acid B, a preferably C₁₆, particularly preferably C₁₋₄,monocarboxylic acid, is preferred. Specifically, at least one memberselected from formic acid, acetic acid, propionic acid, n-butyric acidand isobutyric acid, may be mentioned. Among them, acetic acid orpropionic acid is preferred from the viewpoint of the low corrosivenessto the material of the apparatus and the evaporation latent heat. Morepreferably, it is an acid produced as a byproduct by the fungus to beused for bioconversion. For example, in the case of the fungus disclosedin JP-A-11-206385 or JP2002-34826, acetic acid is preferred. Further,acid B must be volatile, so that it can be separated from the alkalimetal salt. Further, it is preferably stable against heat. Not preferredis one which has a carbon-carbon double bond or triple bond and whichundergoes polymerization or decomposition under a condition of nothigher than 200° C. in the presence of an alkali metal or alkaline earthmetal, or one which has a peroxide as a functional group and whichundergoes self decomposition under a condition of not higher than 200°C. in the presence of an alkali metal or alkaline earth metal, or onewhich has plural functional groups in one molecule such as lactic acid,tartaric acid or an amino acid and which forms a polymer (such as apolyester or polyamide).

As mentioned above, organic acid A is obtained from a fermenter as adilute aqueous solution in the form of a salt with the neutralizingagent employed in the bioconversion. Accordingly, organic acid A isseparated and purified from the reaction solution discharged from thisfermenter, whereby organic acid A as a commercial product can beproduced. Here, a case will be described in which at least one memberselected from the group consisting of ammonia, ammonium carbonate andurea is used as a neutralizing agent (hereinafter sometimes referred toas an ammonia type neutralizing agent).

In such a case, the reaction solution from the fermenter containing anammonium salt of organic acid A is usually a dilute aqueous solution,and this reaction solution is preferably concentrated. The method forconcentration is not particularly limited, and, for example,evaporation, crystallization by means of an alcohol or the like,membrane separation utilizing reverse osmosis, or electrodialysis bymeans of an ion exchange membrane, may be mentioned. Among them,electrodialysis has a difficulty such that a scale merit can not beobtained, and the cost for the apparatus or operation is high, asmentioned above. In the crystallization by means of an alcohol or thelike, an extradistillation apparatus to recover the alcohol will berequired. From such a viewpoint and from the viewpoint of the cost,distillation is preferred, and preferably, distillation by means of amulti-effect evaporator may be mentioned.

With respect to the degree for concentration of the reaction solution,even in the case of an aqueous solution having a high concentration, forexample, a highly concentrated aqueous solution in which theconcentration of an ammonium salt of organic acid A is at least 40 wt %,concentration may be carried out until the ammonium salt of organic acidA precipitates in solid form. In the case of a highly concentratedaqueous solution, there is a merit such that dissolution into acid B iseasy, and the operation is easy as compared with a slurry or solid. Onthe other hand, in a case where the ammonium salt of organic acid A ismade into solid form, mixing of water and acid B can be avoided, andthere is a merit such that even if excess ammonia or an ammonium salt ofacid B formed as byproduct, is present, such ammonia or an ammonium saltcan be removed by vaporization in the drying/evaporation step, forexample, by means of a thin film evaporator. The degree forconcentration is suitably determined so that the entire processincluding the reaction conditions for bioconversion which areinfluential over the types and amounts of impurities, can be optimized.

Depending upon the type of organic acid A or the type of acid B, thereactive crystallization may be carried out in a single stage or inmultiple stages (a plurality of stages). It is usually carried out inmulti-stages from restrictions such as initial investment, operationalconditions or recovery rate, and it is particularly preferably carriedout in from 2 to 4 stages in many cases. Further, in a case wheremulti-stage crystallization is carried out, one having a pH of nothigher than 7, corresponds to the reactive crystallization in thepresent invention. When the pH is not higher than 7, for example, iforganic acid A is succinic acid, a monoammonium salt of succinic acidcan be obtained from a diammonium salt of succinic acid, whereby in thesubsequent reactive crystallization, succinic acid can be obtained at ahigher recovery rate.

Thus, this corresponds to the reactive crystallization. In the finalstage of the reactive crystallization (in the single stage when thereactive crystallization is carried out in a single stage), the amountof acid B to be added to the reaction solution may be an amount suchthat organic acid A will precipitate by the addition of acid B, i.e. anamount which is sufficient for formation of organic acid A by anacid/base reaction of acid B with an ammonium salt of organic acid A andwhich is sufficient to precipitate formed organic acid A withoutdissolution. The amount of acid B varies depending upon the type and pKaof acid B, the type and pKa of organic acid A, the degree ofconcentration of the fermentation reaction solution, etc., and is notparticularly limited. From the viewpoint of the operation efficiency,precipitation efficiency, etc., the amount of acid B to be added is fromabout 1 to 100 times by mol, preferably from 1.5 to 30 times by mol,more preferably from 2 to 20 times by mol, to the ammonium salt oforganic acid A, when the concentrate is in solid form.

Further, the system in which the above organic acid A precipitates, maycontain water. Especially under a condition where ammonia is present ina large amount, in order to dissolve an ammonium salt of acid B to beformed as a byproduct, it may be desirable for the system to containwater in many cases, and water may be added also when the amount of acidB to be used is small.

There is no particular limitation to the conditions for the reactivecrystallization of organic acid A by the addition of acid B. However,usually, acid B may be added to the concentrate of the above-mentionedreaction solution, followed by heating and then the mixture is left tocool. Otherwise, water may be added to dissolve the ammonium salt oforganic acid A, and then acid B is added for crystallization. The lattermethod is effective for organic acid A which has a low solubility inwater in the form of an acid and will have a high solubility when formedinto a salt, so that the difference in solubility is remarkable, likeglutamic acid.

The heating temperature, the heating time and the cooling temperature atthe time of crystallization may vary depending also on the type oforganic acid A in the concentrate, the type and the amount to be addedof acid B, etc. However, it is usually preferred that it is completelydissolved at a temperature of from 60 to 130° C., and then left to coolat a temperature of at most 50° C., preferably at most 40° C. and atleast 0° C., preferably at least 10° C.

In a case where acetic acid is employed as acid B, its melting point is16° C., but the cooling temperature may be lowered to close to 10° C. byan influence of lowering of the solidification point. For a practicalprocess, the cooling temperature is preferably at least 15° C. as a safecondition to avoid solidification of acid B. Especially in the case of acontinuous process, it is preferred that the temperature of utility(cooling medium) of a heat exchanger has a temperature difference byabout 10° C. from the objective temperature, whereby the coolingtemperature is more preferably at least 20° C. when acid B is aceticacid.

The reactive crystallization in the present invention can be carried outin accordance with a usual method by means of a commonly employedcrystallizing apparatus. However, with some organic acid A, particularlywith succinic acid, the crystallization speed is slow, and accordingly,it is preferred to employ some measure to improve the amount ofcrystallization, such as circulating seed crystals or taking a longretention time.

By carrying out the reactive crystallization, organic acid A having alow solubility in acid B will form and precipitate by an acid/basereaction of acid B and an ammonium salt of organic acid A obtained bythe bioconversion employing an ammonia type neutralizing agent.Accordingly, by separating the precipitate from this crystallizationsolution by e.g. filtration, organic acid A having a high purity can berecovered as the desired product. The obtained organic acid A may bepurified, for example, by recrystallization employing e.g. acid B, asthe case requires, to obtain a final product.

Further, in the production of organic acid A by bioconversion, dependingupon the microorganism, the productivity may be changed by theneutralizing agent. Therefore, there may be a case where it is preferredto use an alkali metal and/or alkaline earth metal hydroxide orcarbonate (hereinafter sometimes referred to as an alkali metal oralkaline earth metal type neutralizing agent) rather than the aboveammonia type neutralizing agent, as the neutralizing agent. In a casewhere an alkali metal or alkaline earth metal type neutralizing agent isemployed, organic acid A by bioconversion will be formed in the form ofan alkali metal or alkaline earth metal salt, but the alkali metal oralkaline earth metal is not volatile, whereby it is difficult toseparate organic acid A and the alkali metal or alkaline earth metalsalt of acid B from the mother liquor comprising organic acid A and thealkali metal or alkaline earth metal salt of acid B formed as abyproduct by this reactive crystallization.

Therefore, in a case where an alkali metal or alkaline earth metal typeneutralizing agent is employed, a Solvay method is employed as the firstreactive crystallization step, wherein exchange of the bases is carriedout to obtain an ammonium salt of organic acid A, and this ammonium saltof organic acid A is subjected to reactive crystallization by means ofacid B in the second reactive crystallization step to obtain organicacid A. Also in this case, it is preferred to supply the reactionsolution obtained in the bioconversion step to the first reactioncrystallization step after concentrating it.

In the first reactive crystallization step, firstly, ammonia and carbondioxide and/or ammonium carbonate is added to the concentrate obtainedin the concentration step, to precipitate an alkali metal or alkalineearth metal carbonate from an aqueous solution of an alkali metal oralkaline earth metal salt of organic acid A. In this first reactivecrystallization step, the amount of ammonia and carbon dioxide and/orammonium carbonate to be added, is not particularly limited so long asit is an amount sufficient to precipitate the alkali metal or alkalineearth metal carbonate.

By this first reactive crystallization step, from the alkali metal oralkaline earth metal salt of organic acid A, an alkali metal or alkalineearth metal carbonate will precipitate, and an ammonium salt of organicacid A will form. From the ammonium salt of organic acid A formed in thefirst reactive crystallization step, in the next second reactivecrystallization step, organic acid A can be precipitated by reactivecrystallization by means of acid B in the same manner as in the reactivecrystallization step in the case where the above-mentioned ammonia typeneutralizing agent is employed.

Separation, Recovery and Recycling of Acid B, Organic Acid a andAmmonium Salts Thereof in the Separated Mother Liquor

The separated mother liquor (hereinafter sometimes referred to as “thecrystallization mother liquor” or “the mother liquor”) after separatingorganic acid A from the reactive crystallization solution, contains anammonium salt of organic acid A, an ammonium salt of acid B formed by anacid/base reaction therewith, excess acid B and residual organic acid A.In the present invention, acid B and its ammonium salt are efficientlyseparated from such a separated mother liquor by the following method,whereby the ammonium salt of organic acid A, and organic acid A, can berecovered. Further, the separated ammonium salt of acid B is decomposed,and acid B and ammonia thereby obtained, are reused.

In the present invention, firstly, acid B is vaporized and removed fromthe crystallization mother liquor, followed by further heating tovaporize the ammonium salt of acid B. The vaporization of acid B fromthe crystallization mother liquor is preferably carried out at atemperature of not higher than the melting point of the ammonium salt ofacid B, and it can be carried out by means of e.g. a kettle typeevaporator, a thin film evaporator, a flashed drum having a heatingsection, a combination of a heat exchanger and a flash drum, or acombination thereof. In a case where one having a distillation columnform is employed, if the interior of the column is not higher than themelting point of the ammonium salt of acid B, the crystallization motherliquor may be supplied to any position, such as a condenser section, areflux line, etc. The specification and the form of the apparatus may beany so long as they are under such a condition that acid B can bevaporized at a temperature of not higher than the melting point of theammonium salt of acid B.

The temperature range for vaporization of acid B is preferably at least20° C. and at most the melting point of the ammonium salt of acid B. Themelting point of ammonium acetate as a typical example of the ammoniumsalt of acid B in the present invention, is 114° C. The melting pointhas a specific meaning in the motion of the molecule, and if ammoniumacetate exceeds the melting point, it will be vaporized while beingpyrolized. A boiling point of the ammonium salt of acid B istheoretically necessarily present, and a phenomenon such as sublimationis also involved. It is difficult to strictly divide one due to thepyrolysis and contribution of evaporation or sublimation. Accordingly,vaporization of the ammonium salt of acid B may sometimes be called as“decomposition/vaporization” in the present invention, On the otherhand, ammonium propionate has strong deliquescence, and its meltingpoint is not known. However, taking into consideration the similarity toammonium acetate, it is difficult to simply consider that the differencein the melting point between acetic acid and propionic acid will be thedifference in the melting point of their ammonium salts. However, atemperature slightly lower than 114° C., i.e. about 100° C., is assumedto be the melting point of ammonium propionate.

Melting point of acetic acid: 16.6° C.

Melting point of ammonium acetate: 114° C.

Melting point of propionic acid: −20.8° C.

Thus, the temperature for vaporization of acid B varies also dependingupon the type of acid B (i.e. the type of the ammonium salt of acid B),but it is usually preferably within a range of from 40 to 100° C. At thetime of vaporizing acid B at such a temperature, the operationconditions other than the temperature are not particularly limited.However, with respect to the pressure condition, reduced pressure oratmospheric pressure is preferred, since corrosion of the material ofthe apparatus will be vigorous if the pressure is elevated. Particularlypreferred is a reduced pressure condition of from 10 to 400 mmHg, morepreferably, from 40 to 200 mmHg.

At the time of vaporization of such acid B, substances having meltingpoints lower than acid B contained in the crystallization mother liquor,such as water, etc., will also be vaporized.

Thus, acid B in the crystallization mother liquor is vaporized andrecovered, but from the viewpoint of the subsequent operations, i.e.vaporization of the ammonium salt of acid B, recovery of the residualammonium salt of organic acid A, or organic acid A, etc., the amount ofacid B to be vaporized and removed from the crystallization motherliquor may vary also depending upon the amounts of acid B and othercomponents in the crystallization mother liquor, but the degree ofvaporization may be to such an extent that the mother liquor will be aslurry. If the vaporization is proceeded to obtain solid, in a usualmethod by the second vaporization apparatus, the thermal conductivitytends to deteriorate (e.g. a thin film evaporator), such beingundesirable. As an index, the solubility of organic acid A will besaturated at the temperature for vaporization. The saturated solubilityis determined by the amount of the ammonium salt of acid B correspondingto the amount of ammonia to be removed and the dissolved amount oforganic acid A. In the following, the crystallization mother liquorafter vaporizing acid B will sometimes be referred to as “the firstresidual liquid”.

At the time of vaporization of the ammonium salt of acid B aftervaporizing acid B, the retention time will be important. Namely, as willbe evident from the results of the Test Examples given hereinafter, theamidation reaction will be rapidly accelerated by heating at atemperature of about 120° C. On the other hand, in order to separate theammonium salt of acid B from organic acid A and its ammonium salt, ahigher temperature is required, and a temperature of at least themelting point of the ammonium salt of acid B is particularly preferred.

Accordingly, as a method for vaporizing the ammonium salt of acid B, onehaving a short heating time is preferred in order to prevent a sidereaction such as amidation under such a high temperature condition.Further, it is preferred to carry out the vaporization in a super heatedstate, i.e. to set the process fluid under a reduced pressure condition,to heat it with a heat source having a sufficiently high temperature. Assuch a heat source, steam or heating oil may, for example, be usuallyconsidered. In such a case, the heating temperature is considered to bepreferably at most 200° C., taking into consideration e.g. corrosion byacid B. Otherwise, the temperature may be raised rapidly, for example,by imparting molecular vibration by means of electromagnetic waves.However, the heating temperature may be at least the melting point, andthe retention time may not have the upper limit, so long as it issufficiently short.

Accordingly, with respect to the process fluid, the operable range is atleast 0.001 mmHg (0.133 Pa) and at most 200 mmHg (26.7 kPa), morepreferably at most 100 mmHg (13.3 kPa). More preferably, it is from 20mmHg (2.67 kPa) to 90 mmHg (12.0 kPa).

As an apparatus satisfying such a condition, a thin film evaporator maybe mentioned which is usually suitable for heating under reducedpressure for a short period of time. Further, a heater having a sprayingfunction or an evaporator having a temperature difference between autility and the process fluid of at least 20° C., may, for example, bementioned. The heating method is not particularly limited, and it may bea rapidly heating method by imparting molecular vibration by means ofelectromagnetic waves in the same principle as for a microwave oven. Anyother operation may be employed so long as it satisfies the reducedpressure condition and the high temperature condition, and there is noparticular restriction as to the apparatus, the principle or itsstructure, so long as the heating time is short, and a sufficient heatcan be provided.

The heating temperature may vary also depending upon the type of theammonium salt of acid B or the pressure condition. However, in the caseof ammonium acetate, it is preferably from 115 to 180° C., morepreferably from 120 to 160° C., and in the case of ammonium propionate,it is preferably from 100 to 180° C.

The liquid or slurry (hereinafter sometimes referred to as “the secondresidual liquid”) obtained by vaporizing the ammonium salt of acid Bfrom the first residual liquid in such a manner, contains organic acid Aand its ammonium salt, and residual acid B and its ammonium salt, and itmay be circulated to and treated in the reactive crystallization step tofurther recover organic acid A.

In the present invention, acid B separated by vaporization from thecrystallization mother liquor after precipitating and separating organicacid A in the reactive crystallization of the ammonium salt of organicacid A and acid B, is preferably recycled to and reused in the reactivecrystallization step. This acid B may contain water and othersubstances. Recovered acid B is usually purified and then reused as asolvent for crystallization. However, depending upon the type and amountof the impurity, it may be used as it is as a solvent forcrystallization without carrying out the purification.

Decomposition of the Ammonium Salt of Acid B

The ammonium salt of acid B separated by vaporization from thecrystallization mother liquor, is decomposed into acid B and ammonia.The method for decomposing the ammonium salt of acid B will be describedbelow, but it is not limited to the ammonium salt of acid B obtainedfrom the separated mother liquor of organic acid A, and it is similarlyapplicable to an ammonium salt of acid B obtained from another process.

In the method for decomposing the ammonium salt of acid B in the presentinvention, in a heating step, a liquid containing the ammonium salt ofacid B, an alkali metal or alkaline earth metal, and water, preferably aliquid having an alkali metal or alkaline earth metal salt of acid Badded to a mixed liquid comprising the ammonium salt of acid B and water(hereinafter sometimes referred to as “feed material liquid”) is heatedto withdraw a gas of a basic aqueous solution. Hereinafter, this step ofheating will be referred to as “the heating step”, and the operation atthat time may sometimes be referred to as “the heating operation”.

When the temperature of the gas of a basic aqueous solution withdrawn inthe heating step is higher than the melting point of the ammonium saltof acid B, acid B may partially be withdrawn together. Therefore, thewithdrawn gas of a basic aqueous solution is subjected to gas/liquidseparation, gas/solid separation or gas/liquid/solid separation of theammonium salt of acid B at a temperature of not higher than the meltingpoint of the ammonium salt of acid B under reduced pressure oratmospheric pressure, directly or after condensation. This separatingstep will be hereinafter referred to as “the separation step”, and itsoperation may sometimes be referred to as “the separating operation”.

The alkali metal and/or alkaline earth metal to form the alkali metalsalt and/or alkaline earth metal salt of acid B is preferably at leastone member selected from the group consisting of Na, K, Ca and Mg.Particularly preferred is Na or K.

The apparatus to be used for this heating step may be any apparatus solong as it is one capable of heating operation and capable of separatinga gas phase and a liquid phase. The heating and the gas/liquidseparation may be carried out in separate apparatus or by a combinationof a heat exchanger and a flash drum. In the case of a kettle type heatexchanger, the heating and the gas/liquid separation can be carried outin one apparatus. Further, the heating mechanism is not particularlylimited, and it may, for example, be a flash drum provided with a jacketor a heat conductive coil.

In order to carry out both the heating and the gas/liquid separationefficiently, a distillation column is most preferred. The distillationcolumn may be either a packed column or a plate column, and there is noparticular restriction also with respect to the structure. However, tosecure the retention time as described hereinafter, a plate column ispreferred. Further, the reboiler may be built-in or externally attached.When an external reboiler is employed, it may be a forcibly circulatingtype reboiler, a thermo-siphon type reboiler or a kettle type reboiler,but it is not limited thereto. In the present invention, an operationcarried out by a combination of a distillation column and a reboiler, isregarded as a heating operation.

There is no restriction as to the presence or absence of a condenser,and a condenser is not one which constitutes a part of the heatingoperation. Theoretically, a kettle type heat exchanger or a flash drumequipped with a heating device may be regarded as a single platedistillation column.

The gas withdrawn in the heating step, contains ammonia and necessarilyhas a pH of higher than 7. Accordingly, in this invention, this isreferred to as the heating step for withdrawing a gas of a basic aqueoussolution.

Among apparatus to carry out such a heating operation to withdraw thegas of such a basic aqueous solution, most preferred is a distillationcolumn. Accordingly, the following description will be made with respectto a case where a distillation column is mainly employed.

In order to obtain the effect for separating acid B and water by a salteffect and at the same time to decompose the ammonium salt of acid B, adistillation column is suitable. Ammonia is considered to be not inusual gas/liquid equilibrium (evaporation and condensation are in thesame amount) but be substantially influenced by the retention time andthe size of the gas/liquid interface area, and accordingly, in order tocarry out the heating step more efficiently, secure hold up of theliquid or a longer retention time becomes important. For this purpose,as the distillation column, a plate (tray) column is preferred. Evenwith a packed column, hold up of a liquid may be obtained to someextent, but with a plate (tray) column rather than a packed column, theeffect for separating acid B and water by a salt effect, and the effectfor decomposing the ammonia salt of acid B can be simultaneouslyobtained more certainly.

With respect to the tray type of the plate column, when the operationrange at the time of the start up or shut down is taken intoconsideration, a sieve tray is practically inferior, as weeping islikely to take place. Even if the operation rate is low or 0, a traywhereby a liquid is certainly held on the tray and weeping scarcelyoccurs, is preferred. As such a tray, a bubble tray may be mentioned asone example of a fixed tray. With a bubble tray, in order to improve thegas/liquid contact on the tray, in addition to a weir for downcomer, aweir is present also at gas holes on the tray from the construction ofthe bubble portion, whereby the depth of liquid can be maintained.Further, like a valve cap tray, a tray of the type wherein holes on thetray may be closed by a movable cap, scarcely undergoes weeping and isthus preferably applied to the present invention.

However, when the temperature profile in the interior of the column istaken into consideration, if the temperature becomes high in a statewhere water is little, amidation take place, and therefore, it ispreferred to shorten the retention time at the lower portion of thecolumn where stripping of water is carried out. Therefore, it ispreferred that the upper portion of the column is a plate column, andthe lower portion is a packed column. Their ratio or the plate numbervaries depending upon the temperature or the pressure and may suitablybe optimized.

In order to obtain the effect for separating acid B and water by a salteffect by the entire apparatus, in the case of a distillation column, itis preferred to supply the feed material from the top of the column,i.e. to carry out the separation in the form of so-called extractiondistillation. However, the plate where the feed material is supplied isnot particularly limited.

The pressure of the column is not particularly limited, but forefficient decomposition of the ammonium salt of acid B, it must be apressure such that at least the column bottom temperature will be atleast 80° C., preferably from 115 to 180° C. Further, if the column topis at a temperature lower than whichever is higher between the meltingpoint of the ammonium salt of acid B and the boiling point of acid B,the column top portion can be regarded as a gas/liquid separationapparatus in the separation step after the heating step, whereby itbecomes possible to carry out the heating step and the separation stepin one apparatus, and the number of apparatus can be reduced, such beingdesirable from the viewpoint of the investment cost. The temperaturecondition at the column top in such a case is not higher than 114° C.(the melting point of ammonium acetate) in a case where the ammoniumsalt of acid B is ammonium acetate, or not higher than 141° C. (theboiling point of propionic acid) in the case of ammonium propionate.

The pressure condition to satisfy the conditions of the column topvaries depending upon e.g. the type and the amount of acid B or thealkali metal or alkaline earth metal, the amount of water and thedesired degree for separation of water/acid B, but it is usually at most2.0 atm (0.2 MPa), preferably at most atmospheric pressure (1 atm (0.1MPa)). Further, the pressure condition satisfying the conditions of theabove-mentioned column bottom likewise varies depending upon e.g. thetype and the amount of acid B or the alkali metal or alkaline earthmetal, the amount of water, the desired degree for separation ofwater/acid B, and the pressure loss due to trays or packing material,but it is usually at least 80 mmHg (10.6 kPa), preferably at least 200mmHg (26.7 kPa).

When the feed material is supplied to the column top portion, acid B orits salt may sometimes be distilled off by a stripping effect orentrainment (inclusion of splash). In such a case, even if theconditions for the heating operation and the separating operation can besatisfied solely by a distillation column, it may be necessary to takesome measure such as to lower the supply plate or to additionallyinstall a gas/liquid separation apparatus corresponding to theseparating operation for the purpose of removing the salt by stripping.

Whereas, in a case where a distillation column as one of heatingapparatus and a gas/liquid separating apparatus are separated, the gasof a basic aqueous solution withdrawn from the column top of thedistillation column may once be condensed by a condenser and thensupplied to a gas/liquid, gas/liquid/solid or gas/solid separatingapparatus. Otherwise, as the case requires, a pressure adjustor may beinstalled in the withdrawing line from the column top, so that thecondenser may be made to be a gas/liquid, gas/liquid/solid or gas/solidseparating apparatus. In the former case, the supply to the gas/liquidseparating apparatus will be mainly a liquid, but it may be supplied asgas/liquid. In the latter case, the supply to the gas/liquid separatingapparatus may accompany entrainment (inclusion of splash) but is mostlya gas.

The liquid, solid or slurry withdrawn from the gas/liquid,gas/liquid/solid or gas/solid separating apparatus, is mainly one havingthe ammonium salt of acid B distilled by the stripping effect,concentrated. This concentrate may be returned to the heating apparatusto carry out the heating step, or mixed to an aqueous solution of anammonium salt of acid B to be supplied afresh, or to an aqueous solutionof acid B, and subjected to recycling treatment until it is decomposed.

Either in a case where the distillation column for the heating step andthe gas/liquid, gas/liquid/solid or gas/solid separating apparatus forthe separation step are unitary or in a case where they are separateapparatus, the liquid withdrawn from the bottom of the column isseparated into acid B and the alkali metal or alkaline earth metal saltof acid B by a usual method such as one by means of an evaporator or athin film evaporator. Otherwise, gas withdrawal may be carried out froma recovery portion (a recovery plate) of the distillation column as aheater.

Having been subjected to a heat history by the process up to this stage,the ammonium salt of acid B has been partially amidated. Such an amidecompound has a high boiling point, and the majority takes a behaviorsimilar to an alkali metal or alkaline earth metal salt of acid B. Theboiling point of acetamide as a typical amide compound is 222° C. andwill not substantially be included. Even if such an amide compound isincluded slightly in acid B, for example, by entrainment, it can readilybe separated by a usual method such as distillation.

Such an amide compound will be hydrolyzed by the presence of an alkalimetal or an alkaline earth metal, when water is added, followed byheating. Namely, the alkali metal or alkaline earth metal salt of acid Bis recovered for recycling, and before it is supplied to a heating stepi.e. to a heating apparatus provided separately from a separatingapparatus or to a distillation column as a heating apparatus, or to adistillation apparatus, as mixed to an aqueous solution of an ammoniumsalt of acid B or an aqueous solution of acid B to be supplied afresh,it may be preheated, or it may be heated in the heating apparatus or thedistillation apparatus, whereby the amide compound can be hydrolyzed andremoved.

In the present invention, the type of the alkali metal or alkaline earthmetal is not particularly restricted, and one type may be used alone, ortwo or more types may be used in combination. As between the alkalimetal and the alkaline earth metal, the alkaline earth metal is likelyto take a crosslinked structure and thus has a drawback such that it islikely to bring about a problem of high viscosity or crystallization.Accordingly, an alkali metal is preferred. Among alkali metals, sodiumor potassium is particularly preferred in a case where the product towhich this process is applied, is a food additive or a pharmaceutical,or when economical efficiency or handling efficiency is taken intoconsideration. Further, they may be used as mixed.

The ammonium salt of acid B is heated at a temperature of at least 80°C., preferably from 100 to 160° C., under a condition of at least pH6.5, preferably from pH 7 to pH 10 together with an alkali metal salt(such as a sodium salt or a potassium salt) and/or an alkaline earthmetal salt (such as a magnesium salt or a calcium salt) of acid B in thepresence of a proper amount e.g. from 0.3 to 10 times by weight,preferably from 0.5 to 5 times by weight, to the ammonium salt of acidB, of water, whereby ammonia can be vaporized.

Especially when a reactive distillation apparatus is employed, thecolumn top portion is at least pH 7, and the column bottom portion is atmost pH 7. With respect to such conditions, the ammonium salt of acid Bcan be decomposed by using from 0.3 to 5 times by weight, preferablyfrom 0.5 to 3 times by weight, of water, and from 0.2 to 2 times byweight, preferably from 0.5 to 1.5 times by weight, of an alkali metalsalt (such as a sodium salt or a potassium salt) and/or an alkalineearth metal salt (such as a magnesium salt or a calcium salt) of acid B,to the ammonium salt of acid B.

The smaller the amount of water, the smaller the consumption of energy,but amidation is more likely to take place. Accordingly, it is suitablycontrolled depending upon the type of acid B, the type and amount of thealkali metal or alkaline earth metal, the structure of the apparatus,the retention time distribution, etc.

Further, the method of the present invention can be used also as aneconomically effective method for separating an industrially importantaqueous acetic acid solution, by mixing ammonia to e.g. an aqueousacetic acid solution to obtain an aqueous ammonium acetate solution. Insuch a case, the withdrawn aqueous ammonia or a vapor containing ammoniais separated into pure water and concentrated aqueous ammonia by a usualmethod such as distillation, and the concentrated aqueous ammonia orammonia gas is returned to an aqueous acetic acid solution to besupplied afresh and recycled for use. Thus, this method is particularlyeffective for purification of water having a small acetic acid content.

Further, in the present invention, the liquid after withdrawing the gasof a basic aqueous solution in the heating step, contains mainly freeacid B obtained by decomposition of the alkali metal or alkaline earthmetal salt of acid B and a non-decomposed ammonium salt of acid B. Thisliquid may be heated under reduced pressure or atmospheric pressure,preferably under reduced pressure, more preferably at most 100 mmHg,particularly preferably at most 75 mmHg at a temperature of at least125° C., preferably at least 135° C., more preferably at least 160° C.,particularly preferably from 180 to 220° C., whereby acid B can beseparated and recovered. Acid B thus recovered, can be reused in theabove-mentioned reactive crystallization step. If the operation iscarried out under sufficiently reduced pressure (at most 100 mmHg) at ahigh temperature (at least 180° C.), an acid B amide compound and thenon-reacted ammonium salt of acid B will be vaporized together with acidB. They are separated by a usual method (such as distillation), wherebyacid B having a higher purity can be obtained.

Further, the residue after separating and recovering acid B as describedabove, contains an alkali metal or alkaline earth metal, anon-decomposed ammonium salt of acid B, and an amide compound of acid Bas a byproduct, and such residue can be recycled for use as an alkalimetal or alkaline earth metal source. In such a case, this residuecontains an amide compound of acid B as a byproduct. This amide compoundcan easily be hydrolyzed in the presence of an alkali metal and water.After adding water or a liquid containing acid B and water to the aboveresidue, the amide compound of acid B as a byproduct, can be hydrolyzedat a temperature of at least 125° C., preferably at least 140° C., morepreferably at least 150° C.

Now, with reference to the drawings, specific constructions of apparatussuitable for carrying out the method for decomposing the ammonium saltof acid B, will be described. However, it should be understood that thepresent invention is by no means restricted to the methods shown in thedrawings. Further, in the following, ammonium acetate is exemplified asan ammonium salt of acid B, and sodium is exemplified as an alkali metalor alkaline earth metal. However, it is needless to say that the presentinvention is not limited to ammonium acetate and sodium, but isapplicable to other ammonium salts of acid B and other alkali metals oralkaline earth metals.

In the method of FIG. 1, ammonium acetate and water are supplied to adistillation column 1 via an acetamide decomposition vessel 3. To thisacetamide decomposition vessel 3, a residue (containing sodium acetate,acetamide as byproduct and non-decomposed ammonium acetate) from a thinfilm evaporator 4 of a later stage, is recycled, and this residue ismixed with an aqueous ammonium acetate solution and sent to thedistillation column 1 and introduced to the upper portion of thedistillation column 1. As mentioned above, in this acetamidedecomposition vessel 3, acetamide is mixed with water, wherebyhydrolysis of acetamide is carried out.

The mixed liquid from the acetamide decomposition vessel 3 is subjectedto the heating operation and the separating operation under theabove-described distillation conditions in the distillation column 1,whereby a gas of a basic aqueous solution containing ammonia, water anda small amount of ammonium acetate, will be distilled from the top ofthe distillation column 1. This gas of a basic aqueous solution issubjected to gas/liquid separation at a temperature of not higher thanthe melting point of ammonium acetate in a vaporizer 2, whereby waterand ammonia are separated. Residual ammonium acetate is supplied to theacetamide decomposition vessel 3 and subjected to recycling treatment.

The bottom liquid from the bottom of the distillation column 1, containsacetic acid, non-decomposed ammonium acetate, acetamide as a byproductand sodium acetate. In a thin film evaporator 4, acetic acid isseparated, and the residue is recycled to the acetamide decompositionvessel 3.

The method shown in FIG. 2, is different from the method shown in FIG. 1in that the ammonium acetate distillate from the vaporizer 2 is returnedto the distillation column 1, but the heating operation and theseparating operation are carried out in the same manner as in FIG. 1.

The method shown in FIG. 3 is different from the method shown in FIG. 1in that in the distillation column 1A, vaporization and distillation arecarried out to omit the vaporizer 2, but the heating operation and theseparating operation are carried out in the same manner as in FIG. 1.Further, in this method, the mixed liquid from the acetamidedecomposition vessel 3 may be introduced to the vaporizing section or tothe upper portion of the distilling section in the distillation column1A.

The method shown in FIG. 4 is different from the method shown in FIG. 1in that in the distillation column 1B, acetic acid is withdrawn from anintermediate plate to carry out also separation of acetic acid therebyto omit a thin film evaporator 4, but the heating and separatingoperations are carried out in the same manner as in FIG. 1.

The method shown in FIG. 5 is different from the method shown in FIG. 1in that a flash drum 5 is employed instead of the distillation column,but the heating and separating operations are carried out in the samemanner as in FIG. 1.

In any one of these methods, by the presence of an alkali metal or analkaline earth metal, and ammonia, in the heating step such as in thedistillation column or flash drum, the reflux ratio will be small, andit is possible to substantially reduce the energy consumed in theheating and separating operations.

Recycling of Separated Mother Liquor

In the present invention, in a case where the reactive crystallizationis carried out in multi stages, a mother liquor in a later stagereactive crystallization is mixed with an ammonium salt of organic acidA to be supplied afresh, as a recycling liquid as shown in the following(1) to (3).

(1) The later stage mother liquor is recycled as it is and mixed with anammonium salt of organic acid A to be supplied afresh. In this laterstage mother liquor, acid B and its ammonium salt, and organic acid Aand its ammonium salt, are contained. Among them, acid B will be reactedwith the ammonium salt of organic acid A to be supplied, thereby to beconverted to an ammonium salt of acid B and to precipitate organic acidA monoammonium salt, and in the next vaporization step, it will be isremoved together with the ammonium salt of acid B in the later stagemother liquor. Whereas, organic acid A and its ammonium salt will beseparated as organic acid A and/or its monoammonium salt in the reactivecrystallization together with the ammonium salt of organic acid A to besupplied afresh.

(2) From the later stage mother liquor, acid B is vaporized, separatedand recovered, and then the residue is recycled and mixed with anammonium salt of organic acid A to be supplied afresh.

In this case, it is preferable to retain acid B in the residue to suchan extent that the residue after vaporization and separation willmaintain a liquid phase. Namely, it is necessary that in the recycledliquid, acid B is present in such an amount that the ammonium salt ofacid B, organic acid A and its ammonium salt can sufficiently bedissolved therein.

Also in this case, as in the case of (1), acid B in the recycled liquidwill be reacted with the ammonium salt of organic acid A to be suppliedafresh, and converted to an ammonium salt of acid B, which will beremoved in the next vaporization step together with the ammonium salt ofacid B in the later stage mother liquor. Whereas, organic acid A and itsammonium salt are separated as organic acid A and/or its monoammoniumsalt in the reactive crystallization together with an ammonium salt oforganic acid A to be supplied afresh.

(3) From the separated mother liquor, acid B is vaporized, separated andrecovered, and then the ammonium salt of acid B is vaporized andseparated from organic acid A and its ammonium salt, and the distillateof the ammonium salt of acid B is recycled and mixed with an ammoniumsalt of organic acid A to be supplied afresh.

In this case, it is necessary that in the distillate of the ammoniumsalt of acid B, acid B is contained to such an extent that thisdistillate will maintain a liquid phase. Namely, it is necessary that inthe recycled liquid, acid B is present in such an amount that theammonium salt of acid B can sufficiently be dissolved therein.

Also in this case, as in the case of (1), acid B in the recycled liquid,will be reacted with an ammonium salt of organic acid A to be suppliedafresh, and converted to an ammonium salt of acid B, which will beremoved in the next vaporization step together with the ammonium salt ofacid B in the crystallization mother liquor.

Further, the condition for vaporizing acid B from the crystallizationmother liquor, is the same as in the case of the above (2). Further, tovaporize the ammonium salt of acid B to separate it from organic acid Aand its ammonium salt, it is preferred to employ the same operationalcondition as in the after-mentioned vaporization step. Organic acid Aand its ammonium salt separated by this method, are recycled and treatedin the reactive crystallization step to recover organic acid A. Thecondition for mixing the recycled liquid of the above (1) to (3) withthe ammonium salt of organic acid A to be supplied afresh, is notparticularly limited, the mixing can be carried out by stirring in amixing vessel at a temperature of from 20 to 140° C., preferably from 40to 110° C.

Applications of Organic Acid A

Organic acid A as the desired product obtained by the method of thepresent invention is useful for various applications. Among them,dicarboxylic acids are useful as raw materials for polyesters orpolyamides.

For example, oxalic acid, succinic acid, itaconic acid, glutaric acid,adipic acid, sebacic acid, dodecanoic acid, or lower alcohol estersthereof, succinic anhydride, adipic anhydride, etc., as dicarboxylicacids to be produced by the present invention, are raw materials forhigh molecular weight polyesters. Particularly from the aspect of thephysical properties of the polymer, succinic acid, adipic acid, sebacicacid or an anhydride thereof, is preferred, and such an acid can beproduced by the present invention without giving a burden to theenvironment by a microbial fermentation method from a natural carbonsource.

Further, a diol to be used for e.g. production of a polyester copolymer,such as 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,4-cyclohexanediol or 1,6-cyclohexanedimethanol, may also be obtainedby hydrogenating the above-mentioned organic acid A produced by thepresent invention.

SPECIFIC PREFERRED EMBODIMENTS

Specific preferred embodiments of the present invention are as follows.

1. A method for producing a dicarboxylic acid and/or tricarboxylic acidby bioconversion of a carbon source, which comprises:

a bioconversion step in which a carbon source is converted by amicroorganism in the presence of at least one neutralizing agentselected from the group consisting of ammonia, ammonium carbonate andurea, to obtain a reaction solution containing an ammonium salt of adicarboxylic acid and/or tricarboxylic acid;

a reactive crystallization step in which reactive crystallization iscarried out by adding a monocarboxylic acid to the ammonium salt of adicarboxylic acid and/or tricarboxylic acid obtained in thebioconversion step, to precipitate the desired dicarboxylic acid and/ortricarboxylic acid; and

a separation step in which the dicarboxylic acid and/or tricarboxylicacid precipitated in the reactive crystallization step, is separated.

2. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 1, which includes a concentration step ofconcentrating the reaction solution obtained in the bioconversion step,and wherein the concentrate obtained in the concentration step issupplied to the reactive crystallization step.3. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 1 or 2, which includes an ammonia recovery stepin which the monocarboxylic acid is vaporized and removed from theliquid after separating the dicarboxylic acid and/or tricarboxylic acidin the separation step, then an ammonium salt of the monocarboxylic acidin the liquid is vaporized and collected, the ammonium salt of themonocarboxylic acid is mixed with water and an alkali metal and/oralkaline earth metal salt of the monocarboxylic acid, followed byheating to vaporize and recover ammonia; and

a recycling step in which the ammonia recovered in the ammonia recoverystep, is used as a neutralizing agent in the above bioconversion step.

4. A method for producing a dicarboxylic acid and/or tricarboxylic acidby bioconversion of a carbon source, which comprises:

a bioconversion step in which a carbon source is converted by amicroorganism in the presence of at least one neutralizing agentselected from the group consisting of an alkali metal hydroxide, analkaline earth metal hydroxide, an alkali metal carbonate and analkaline earth metal carbonate, to obtain a reaction solution containingan alkali metal and/or alkaline earth metal salt of a dicarboxylic acidand/or tricarboxylic acid;

a first reactive crystallization step in which reactive crystallizationis carried out by adding ammonia and carbon dioxide, and/or ammoniumcarbonate, to the alkali metal and/or alkaline earth metal salt of adicarboxylic acid and/or tricarboxylic acid obtained in thebioconversion step, to precipitate a carbonate of the alkali metaland/or alkaline earth metal, and the carbonate is separated to obtain anaqueous solution of an ammonium salt of the dicarboxylic acid and/ortricarboxylic acid;

a second reactive crystallization step in which reactive crystallizationis carried out by adding a monocarboxylic acid to the liquid afterremoving the carbonate of the alkali metal and/or alkaline earth metalprecipitated in the first reactive crystallization step, to precipitatethe desired dicarboxylic acid and/or tricarboxylic acid; and

a separation step in which the dicarboxylic acid and/or tricarboxylicacid precipitated in the second reactive crystallization step, isseparated.

5. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 4, which includes a concentration step ofconcentrating the reaction solution obtained in the bioconversion step,and wherein the concentrate obtained in the concentration step issupplied to the first reactive crystallization step.6. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 4 or 5, which includes an ammonia recovery stepin which the monocarboxylic acid is vaporized and removed from theliquid after separating the dicarboxylic acid and/or tricarboxylic acidin the separation step, then an ammonium salt of the monocarboxylic acidin the liquid is vaporized and collected, the ammonium salt of themonocarboxylic acid is mixed with water and an alkali metal and/oralkaline earth metal salt of the monocarboxylic acid, followed byheating to vaporize and recover ammonia; and

a recycling step in which the ammonia recovered in the ammonia recoverystep, is used as an ammonia source in the above first reactivecrystallization step.

7. A method for producing a dicarboxylic acid and/or tricarboxylic acidwherein a dicarboxylic acid and/or tricarboxylic acid is obtained froman ammonium salt of a dicarboxylic acid and/or tricarboxylic acid, whichcomprises:

a reactive crystallization step in which reactive crystallization iscarried out by adding a monocarboxylic acid to the ammonium salt of adicarboxylic acid and/or tricarboxylic acid, to precipitate thedicarboxylic acid and/or tricarboxylic acid;

a separation step in which the dicarboxylic acid and/or tricarboxylicacid precipitated in the reactive crystallization step, is separated;

a step for recovering ammonia and the monocarboxylic acid, in which anammonium salt of the monocarboxylic acid is separated from the liquidcontaining the ammonium salt of the monocarboxylic acid after separatingthe dicarboxylic acid and/or tricarboxylic acid in the separation step,and then, an alkali metal and/or alkaline earth metal salt of themonocarboxylic acid is added to this separated ammonium salt of themonocarboxylic acid to obtain the monocarboxylic acid and ammonia; and

a recycling step in which the ammonia and monocarboxylic acid recoveredin the step for recovering ammonia and the monocarboxylic acid, are usedas an ammonia source for the ammonium salt of the dicarboxylic acidand/or tricarboxylic acid and as the monocarboxylic acid in the abovereactive crystallization step, respectively.

8. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 7, wherein the ammonium salt of the dicarboxylicacid and/or tricarboxylic acid is obtained by bioconversion of a carbonsource employing, as a neutralizing agent, at least one member selectedfrom the group consisting of ammonia, ammonium carbonate and urea.9. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 7, wherein the ammonium salt of the dicarboxylicacid and/or tricarboxylic acid, is obtained by a Solvay method in whichthe ammonium salt of the dicarboxylic acid and/or tricarboxylic acid isobtained from an alkali metal and/or alkaline earth metal salt of thedicarboxylic acid and/or tricarboxylic acid obtained by bioconversion ofa carbon source employing, as a neutralizing agent, at least one memberselected from the group consisting of an alkali metal hydroxide, analkaline earth metal hydroxide, an alkali metal carbonate and analkaline earth metal carbonate.10. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to any one of Items 1 to 9, wherein the carbon number ofthe dicarboxylic acid and/or tricarboxylic acid is from 4 to 12.11. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 10, wherein the dicarboxylic acid and/ortricarboxylic acid is at least one member selected from the groupconsisting of succinic acid, adipic acid, malic acid, tartaric acid,fumaric acid, maleic acid, citric acid, asparaginic acid and glutamicacid.12. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to any one of Items 1 to 11, wherein the carbon number ofthe monocarboxylic acid is from 1 to 6.13. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 12, wherein the monocarboxylic acid is aceticacid and/or propionic acid.14. A method for producing a dicarboxylic acid and/or tricarboxylic acidin which a dicarboxylic acid and/or tricarboxylic acid is obtained froman ammonium salt of the dicarboxylic acid and/or tricarboxylic acid,which comprises:

a reactive crystallization step in which reactive crystallization iscarried out by adding a monocarboxylic acid to the ammonium salt of thedicarboxylic acid and/or tricarboxylic acid, to precipitate thedicarboxylic acid and/or tricarboxylic acid;

a separation step in which the dicarboxylic acid and/or tricarboxylicacid precipitated in the reactive crystallization step, is separated;

a first vaporization step in which the monocarboxylic acid is furthervaporized from the crystallization mother liquor after separating thedicarboxylic acid and/or tricarboxylic acid in the separation step;

a second vaporization step in which an ammonium monocarboxylate isvaporized from the crystallization mother liquor after the firstvaporization step.

15. The method for producing a dicarboxylic acid and/or a tricarboxylicacid according to Item 14, wherein the is first vaporization step is astep of vaporizing the monocarboxylic acid from the crystallizationmother liquor at a temperature of not higher than the melting point ofthe ammonium monocarboxylate.16. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 14 or 15, wherein the second vaporization step isa step of vaporizing the ammonium monocarboxylate by heating the abovecrystallization mother liquor under a reduced pressure of from 0.001mmHg (0.133 Pa) to 200 mmHg (26.7 kPa).17. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to any one of Items 14 to 16, in which the carbon numberof the dicarboxylic acid and/or tricarboxylic acid is from 4 to 12.18. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 17, wherein the dicarboxylic acid and/ortricarboxylic acid is at least one member selected from the groupconsisting of succinic acid, adipic acid, malic acid, tartaric acid,fumaric acid, maleic acid, citric acid, asparaginic acid, glutaric acidand glutamic acid.19. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to any one of Items 14 to 18, wherein the carbon numberof the monocarboxylic acid is from 1 to 6.20. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 19, wherein the monocarboxylic acid is aceticacid and/or propionic acid.21. A method for producing a dicarboxylic acid and/or tricarboxylic acidin which a dicarboxylic acid and/or tricarboxylic acid is obtained froman ammonium salt of the dicarboxylic acid and/or tricarboxylic acid,which comprises:

a reactive crystallization step in which reactive crystallization iscarried out by adding a monocarboxylic acid to the ammonium salt of thedicarboxylic acid and/or tricarboxylic acid, to precipitate thedicarboxylic acid and/or tricarboxylic acid;

a supplying step in which the ammonium salt of the dicarboxylic acidand/or tricarboxylic acid is supplied to the reactive crystallizationstep; and

a separation step in which the dicarboxylic acid and/or tricarboxylicacid precipitated in the reactive crystallization step, is separated;and which includes:

a recycling step in which the crystallization mother liquor afterseparating the dicarboxylic acid and/or tricarboxylic acid in theseparation step, is recycled to the above supplying step;

a mixing step in which the recycled liquid in the recycling step ismixed with an ammonium salt of the dicarboxylic acid and/ortricarboxylic acid supplied afresh in the supplying step; and

a vaporization step in which an ammonium salt of the monocarboxylic acidis vaporized from the mixture obtained in the mixing step, wherein theresidue after vaporizing and removing the ammonium salt of themonocarboxylic acid in the vaporization step, is supplied to the abovereactive crystallization step.

22. A method for producing a dicarboxylic acid and/or tricarboxylic acidin which a dicarboxylic acid and/or tricarboxylic acid is obtained froman ammonium salt of the dicarboxylic acid and/or tricarboxylic acid,which comprises:

a reactive crystallization step in which reactive crystallization iscarried out by adding a monocarboxylic acid to the ammonium salt of thedicarboxylic acid and/or tricarboxylic acid, to precipitate thedicarboxylic acid and/or tricarboxylic acid;

a supplying step in which the ammonium salt of the dicarboxylic acidand/or tricarboxylic acid is supplied to the reactive crystallizationstep; and

a separation step in which the dicarboxylic acid and/or tricarboxylicacid precipitated in the reactive crystallization step, is separated;and which includes:

a monocarboxylic acid recovery step in which the monocarboxylic acid isvaporized and separated from the crystallization mother liquor afterseparating the dicarboxylic acid and/or tricarboxylic acid in theseparation step;

a recycling step in which the residual liquid after removing themonocarboxylic acid in the monocarboxylic acid recovery step, isrecycled to the above supplying step;

a mixing step in which the recycled liquid in the recycling step, ismixed with an ammonium salt of the dicarboxylic acid and/ortricarboxylic acid supplied afresh in the supplying step; and

a vaporization step in which the ammonium salt of the monocarboxylicacid is vaporized from the mixture obtained in the mixing step, in whicha residue after vaporizing and removing the ammonium salt of themonocarboxylic acid in the vaporization step, is supplied to the abovereactive crystallization step.

23. A method for producing a dicarboxylic acid and/or tricarboxylic acidin which a dicarboxylic acid and/or tricarboxylic acid is obtained froman ammonium salt of the dicarboxylic acid and/or tricarboxylic acid,which comprises:

a reactive crystallization step in which reactive crystallization iscarried out by adding a monocarboxylic acid to the ammonium salt of thedicarboxylic acid and/or tricarboxylic acid, to precipitate thedicarboxylic acid and/or tricarboxylic acid;

a supplying step in which the ammonium salt of the dicarboxylic acidand/or tricarboxylic acid is supplied to the reactive crystallizationstep; and

a separation step in which the dicarboxylic acid and/or tricarboxylicacid precipitated in the reactive crystallization step, is separated,and which includes:

a first recovery step in which the monocarboxylic acid is vaporized andseparated from the crystallization mother liquor after separating thedicarboxylic acid and/or tricarboxylic acid in the separation step;

a second recovery step in which the dicarboxylic acid and/ortricarboxylic acid, and its ammonium salt, are separated from theresidual liquid after removing the monocarboxylic acid in the firstrecovery step;

a recycling step in which the residual liquid after separating thedicarboxylic acid and/or tricarboxylic acid, and its ammonium salt inthe second recovery step, is recycled to the above supplying step;

a mixing step in which the recycled liquid in the recycling step, ismixed with an ammonium salt of the dicarboxylic acid and/ortricarboxylic acid supplied afresh in the supplying step; and

a vaporization step in which the ammonium salt of the monocarboxylicacid is vaporized from the mixture obtained in the mixing step, in whichthe residue after vaporizing and removing the ammonium salt of themonocarboxylic acid in the vaporization step, is supplied to the abovereactive crystallization step.

24. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to any one of Items 21 to 23, wherein the mols of themonocarboxylic acid in the recycled liquid to the mols of thedicarboxylic acid and/or tricarboxylic acid supplied afresh in the abovemixing step, are at most 30 times.25. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to any one of Items 21 to 24, wherein the vaporizationstep is a step of vaporizing the ammonium salt of the monocarboxylicacid by heating the above mixture under a reduced pressure of from 0.001mmHg (0.133 Pa) to 200 mmHg (26.7 kPa).26. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to any one of Items 21 to 25, wherein the carbon numberof the dicarboxylic acid and/or tricarboxylic acid is from 4 to 12.27. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 26, wherein the dicarboxylic acid and/ortricarboxylic acid is at least one member selected from the groupconsisting of succinic acid, adipic acid, malic acid, tartaric acid,fumaric acid, maleic acid, citric acid, asparaginic acid, glutaric acidand glutamic acid.28. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to any one of Items 21 to 27, wherein the carbon numberof the monocarboxylic acid is from 1 to 6.29. The method for producing a dicarboxylic acid and/or tricarboxylicacid according to Item 28, wherein the monocarboxylic acid is aceticacid and/or propionic acid.30. A method for decomposing an ammonium salt of a monocarboxylic acidto separate and recover a monocarboxylic acid and ammonia, whichcomprises a heating step in which a liquid containing an ammonium saltof a monocarboxylic acid, an alkali metal and/or alkaline earth metaland water, is heated to withdraw a gas of a basic aqueous solution, anda separation step in which the gas of a basic aqueous solution withdrawnfrom the heating step is, directly or after condensation, subjected togas/liquid separation, gas/solid separation or gas/liquid/solidseparation at a temperature of not higher than the melting point of theammonium salt of the monocarboxylic acid.31. The method for decomposing an ammonium salt of a monocarboxylic acidaccording to Item 30, in which a liquid containing the ammonium salt ofa monocarboxylic acid, an alkali metal salt and/or alkaline earth metalsalt of the monocarboxylic acid, or ions derived therefrom, and water,is supplied to a distillation column, and the gas of a basic aqueoussolution, is withdrawn from the top of the distillation column.32. The method for decomposing an ammonium salt of a monocarboxylic acidaccording to Item 30 or 31, wherein the alkali metal and/or alkalineearth metal is at least one member selected from the consisting of Na,K, Ca and Mg.33. The method for decomposing an ammonium salt of a monocarboxylic acidaccording to any one of Items 30 to 32, wherein the monocarboxylic acidis at least one member selected from the group consisting of aceticacid, propionic acid and butyric acid.34. The method for decomposing an ammonium salt of a monocarboxylic acidaccording to any one of Items 30 to 33, which includes a monocarboxylicacid recovery step in which a liquid after withdrawing the gas of abasic aqueous solution in the heating step, is heated at a temperatureof at least 125° C. under reduced pressure or atmospheric pressure, toseparate and recover the monocarboxylic acid.35. The method for decomposing an ammonium salt of a monocarboxylic acidaccording to Item 34, wherein an ammonium salt of a monocarboxylic acidand water are mixed to the residue after separating the monocarboxylicacid in the monocarboxylic acid recovery step, and the mixture isrecycled to the above heating step.36. The method for decomposing an ammonium salt of a monocarboxylic acidaccording to Item 35, wherein an ammonium salt of a monocarboxylic acidand water are mixed to the above residue, and then the mixture ispreheated at a temperature of at least 90° C. and then recycled to theabove heating step.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples.

TABLE 1 Iso- Solubility Pyne elec- at Organic tric 25° C. Chemistrypoint g/100 MW m.p. pKa1 pKa2 pKa3 pI g H₂O Asparagine 132.12 236 2.025.41 3.11 Aspartic acid 133.1 269 2.1 3.86 2.98 0.5 Glutamic acid 147.13247 2.1 4.07 3.08 0.843 Glutamine 146.15 186 2.17 5.7 3.6 Histidine155.16 287 1.77 7.64 4.29 Isoleucine 131.18 284 2.32 6.04 4.117 Leucine131.18 337 2.33 6.04 2.19 Methionine 149.21 283 2.28 5.74 3.35Phenylalanine 165.19 283 2.58 5.91 2.965 Tryptophan 204.23 289 2.38 5.881.14 Tyrosine 181.19 344 2.2 5.66 0.045 Valine 117.15 315 2.29 6 8.85Fumaric acid 116.07 299.5 3.03 4.44 Tartaric acid 150.09 205 3.04 4.37Succinic acid 118.09 188 4.21 5.64 Maleic acid 116.07 141 1.83 6.07Malic acid 134.09 132 3.40 5.11 o-Phthalic acid 166.13 210 2.95 5.41Glutaric acid 147.13 — 4.31 5.41 Adipic acid 146.14 153.4 4.43 5.41Citric acid 192.13 153 3.13 4.76 6.4 Suberic acid 174.2 142.1 4.52Terephthalic 166.13 3.51 4.82 acid Acetic acid pKa 4.76 Propionic acidpKa 4.86

-   -   pKa of dicarboxylic acids and of propionic acid: Handbook of        Chemistry and Physics

In the following Example 1-1, diammonium succinate (manufactured by WakoPure Chemical Industries, Ltd.) was used as a substitute material for aconcentrate obtained by concentrating, in the concentration step, theammonium salt of organic acid A obtained from a bioconversion step.Further, as acid B, acetic acid (manufactured by Wako Pure ChemicalIndustries, Ltd.) or propionic acid (manufactured by Wako Pure ChemicalIndustries, Ltd.) was used.

Example 1-1

180 g of diammonium succinate (succinic acid: 78 wt %, ammonia: 22 wt %)was dissolved in 720 g of water to prepare 900 g of a 20 wt % ammoniumsuccinate solution.

This aqueous solution was evaporated and concentrated in an oil bath of140° C. (the interior of the evaporator: 100° C.) to a level of 256.5 g.249 g was taken therefrom, and 173 g of acetic acid was added tosuccinic acid, followed by thorough stirring. The mixture (415.5 gcharge) was put into a crystallization apparatus and maintained at 100°C. for 10 minutes, and then maintained at 40° C. for 18 hours withstirring.

Then, vacuum filtration was carried out, and then the solid content wastaken out. The filtrate was 296.6 g, and the solid content was 93.4 g.The obtained solid content was analyzed for organic substances by liquidchromatography and for ammonia by ion chromatography, whereby aceticacid was 28.4 wt %, succinic acid was 58.3 wt %, and ammonia was 10.4 wt%. The total was not 100%, and this is believed attributable to ameasurement error, as ammonia and organic substances were analyzedseparately. Likewise, the mother liquor was found to comprise 59.9 wt %of acetic acid, 25.3 wt % of succinic acid and 6.7 wt % of ammonia.

It is hardly believed that the mother liquor contained such a largeamount of acetic acid, and it is believed that a substantial amount ofammonium acetate was coprecipitated. Therefore, the molar ratios (on theassumption of 100 g) were calculated and found to be as follows.

-   -   Acetic acid: 28.4/60=0.473 Carboxylic acid: 47 mol    -   Succinic acid: 58.3/118=0.494 Carboxylic acid: 98 mol (49×2)    -   Ammonia 10.4/17=0.611 Ammonia: 61 mol

If it is assumed that 60% of acetic acid is in the form of ammoniumacetate (28 mol), ammonia is 33 mol to 98 mol of carboxylic acid ofsuccinic acid, whereby 16 mol (⅓ of the obtained solid) is alreadysuccinic acid itself formed by the salt decomposition, and the rest is amonoammonium salt of succinic acid. In reality, the mother liquor alsocontained ammonia, and it is believed that the salt decompositionproceeded more by the reactive crystallization.

Further, 90 g of the obtained solid was dissolved in 80 g of acetic acidat a temperature of about 80° C., and the solution (165 g) was put intoa crystallizing apparatus and maintained at 80° C. for 10 minutes, andthen maintained at 40° C. for 7 hours with stirring.

Then, vacuum filtration was carried out, and then, a solid content wastaken out. The filtrate was 129.6 g, and the solid content was 16.2 g.The obtained solid content was analyzed for organic substances by liquidchromatography and for ammonia by ion chromatography, whereby aceticacid was 10.9 wt %, succinic acid was 87.4 wt % and ammonia was 2.8 wt%. Likewise, the mother liquor was found to comprise 90.2 wt % of aceticacid, 25.2 wt % of succinic acid and 6.0 wt % of ammonia.

-   -   Acetic acid: 10.9/60=0.182 Carboxylic acid: 18 mol    -   Succinic acid: 87.4/118=0.741 Carboxylic acid: 148 mol (74×2)    -   Ammonia 2.8/17=0.165 Ammonia: 16 mol

In this Example, it was possible to obtain succinic acid from ammoniumsuccinate without employing electrodialysis or an inorganic acid,whereby it was confirmed that decomposition to succinic acid was carriedout solely by reactive crystallization.

Example 1-2

Using a 100 ml reagent bottle, 15.2 g (0.1 mol) of diammonium succinatewas mixed to 15.2 g (0.25 mol) of acetic acid and 6 g of water underheating and dissolved at 90° C. This solution was left for 12 hours in awater bath (40° C.). White solid thereby precipitated was collected byfiltration. The recovered solid was 6.1 g, and as a result of theanalysis, succinic acid was 69 wt %, and ammonia was 12.8 wt %.

3.1 g of this solid was again put into a 100 ml reagent bottle and mixedwith 5.4 g of acetic acid under heating and dissolved at 75° C. Thissolution was left to stand for 8 hours in a water bath (40° C.). Whitesolid precipitated, was collected by filtration. The recovered solid was0.5 g, and as a result of the analysis, succinic acid was 97 wt %, andammonia was 1.6 wt %.

Example 1-3

Using a 100 ml reagent bottle, 15 g (0.1 mol) of diammonium succinatewas mixed with 35 g (0.58 mol) of acetic acid and 10 g of water underheating and dissolved at 95° C. This solution was left to stand for 12hours in a water bath (40° C.). White solid precipitated, was collectedby filtration. The recovered solid was 4.3 g.

4 g of this solid was again put into a 100 ml reagent bottle and addedto 16 g of acetic acid under heating and dissolved at 70° C. Thissolution was left to stand at room temperature (about 15° C.) for 8hours. White solid precipitated was collected by filtration. Therecovered solid was 2.2 g, and as a result of the analysis, succinicacid was 90 wt %, and ammonia was 0.8 wt %.

From the foregoing results, it is evident that it was possible torecover succinic acid of high purity by reactive crystallization bymeans of acetic acid.

Example 1-4

50.35 g of diammonium succinate and 269.72 g of acetic acid were putinto a crystallizing apparatus, dissolved at 85° C. and maintained for10 minutes, and then cooled to 15° C. with stirring. Upon expiration of22 minutes after cooling to 15° C., 1.03 g of reagent succinic acid(manufactured by Wako Pure Chemical Industries, Ltd.) was put as seedcrystals, and the mixture was maintained for 4 hours.

A filtrate was 299.8 g, and a solid was recovered in an amount of 13.1g. The obtained solid content was analyzed for organic substances byliquid chromatography and for ammonia by ion chromatography, wherebyacetic acid was 19.5 wt %, succinic acid was 82.4 wt %, and ammonia was1.1 wt %. Likewise, the mother liquor was found to comprise 80.7 wt % ofacetic acid, 9.9 wt % of succinic acid and 4.0 wt % of ammonia.

-   -   Recovery rate of succinic acid:        (13.1×0.824)/(50.35×118/152)=0.276 (27.6% recovery)    -   Solid molar composition:        -   Succinic acid 13.1×0.824/118=0.0915        -   Acetic acid 13.1×0.195/60=0.0425        -   Ammonia 13.1×0.011/17=0.0084

Example 1-5

50.46 g of diammonium adipate (manufactured by Wako Pure ChemicalIndustries, Ltd.) and 269.83 g of acetic acid were put into acrystallizing apparatus, dissolved at 85° C. and maintained for 10minutes, and then cooled to 15° C. with stirring. Precipitation startedimmediately, and the system was left to stand for 4 hours and 23minutes.

A filtrate was 253.4 g, and a solid was recovered in an amount of 55.4g. The obtained solid content was analyzed for organic substances byliquid chromatography and for ammonia by ion chromatography, wherebyacetic acid was 47.1 wt %, adipic acid was 61.8 wt % and ammonia was 2.0wt %. Likewise, the mother liquor was found to comprise 85.0 wt % ofacetic acid, 5.1 wt % of adipic acid and 3.7 wt % of ammonia.

-   -   Recovery rate of adipic acid:        (55.4×0.618)/(50.465×150.1/184.2)=0.832 (83.2% recovery)    -   Solid molar composition:        -   Adipic acid 55.4×0.618/150.1=0.228        -   Acetic acid 55.4×0.471/60=0.434        -   Ammonia 55.4×0.02/17=0.065

50.21 g of the obtained solid content was washed at 16° C. for 30minutes by using 149.78 g of acetic acid, followed by filtration. Theobtained solid was 25.9 g, and the rinsing liquid was 169.5 g. The solidwas analyzed, whereby acetic acid was 11.6 wt %, adipic acid was 80.3 wt% and ammonia was 0.2 wt %. Likewise, the rinsing liquid was found tocomprise 89.4 wt % of acetic acid, 3.9 wt % of adipic acid and 0.5 wt %of ammonia.

-   -   Recovery rate of adipic acid:        (25.9×0.803)/(50.46×150.1/184.2)=0.505 (50.5% recovery)    -   Solid molar composition:        -   Adipic acid 25.9×0.803/150.1=0.139        -   Acetic acid 25.9×0.116/60=0.050        -   Ammonia 25.9×0.002/17=0.003

Example 1-6

6.08 g of monoammonium glutamate (manufactured by Sigma Co.) wasdissolved in 10.08 g of water. 399.69 g of acetic acid was put into acrystallizing apparatus and maintained at 60° C., and 15.72 g of theaqueous monoammonium glutamate solution was introduced thereinto.Turbidity started immediately, and the system was cooled to 16° C. withstirring. The system was left to stand at 16° C. for 4 hours and 18minutes.

A filtrate was 387.1 g, and a solid was recovered in an amount of 19.3g. The obtained solid content was analyzed for organic substances byliquid chromatography and for ammonia by ion chromatography, wherebyacetic acid was 68.2 wt %, glutamic acid was 24.7 wt % and ammonia was0.15 wt %. Likewise, the mother liquor was found to comprise 92.3 wt %of acetic acid, no glutamic acid detected and 1.4 wt % of ammonia. Therest of the mother liquor is assumed to be water.

-   -   Recovery rate of glutamic acid:        (19.3×0.247)/(6.08×197.1/214.2×15.72/16.16)=0.876 (87.6%        recovery)    -   Solid molar composition:        -   Glutamic acid 19.3×0.247/197.1=0.0247        -   Acetic acid 19.3×0.682/60=0.224        -   Ammonia 19.3×0.0015/17=0.0017

Example 1-7

Using a 100 ml reagent bottle, 50.42 g of 28% aqueous ammonia(manufactured by Kanto Kagaku K.K.) (0.83 mol of ammonia) was added to15 g (0.086 mol) of suberic acid (manufactured by Acros Organics Co.)for dissolution. This solution was dried at 80° C. under reducedpressure to obtain a salt. Upon the analysis, suberic acid was 77 wt %,and ammonia was 9.2 wt %, and it was found that 62% of the carboxylgroup of suberic acid became an ammonium salt.

5.01 g of this ammonium salt of suberic acid was dissolved in 25.05 g ofacetic acid under heating, and this solution was left to stand in aconstant temperature vessel at 15° C. for 18 hours. White solidprecipitated, was collected by filtration. The recovered solid was is0.46 g, and as a result of the analysis, suberic acid was 55 wt %,acetic acid was 40 wt % and ammonia was 0.2 wt %. The mother liquor was29.60 g, and as a result of the analysis, suberic acid was 2.6 wt %,acetic acid was 93 wt % and ammonia was 1.3 wt %.

-   -   Recovery rate of suberic acid: (0.46×0.55)/(5.01×0.62)=0.081        (8.1% recovery)    -   Solid molar composition:

Suberic acid 0.46 × 0.55/174 = 0.00145 Acetic acid 0.46 × 0.40/60 =0.00307 Ammonia 0.46 × 0.002/17 = 0.00005

Example 1-8

50.20 g of diammonium adipate (manufactured by Wako Pure ChemicalIndustries, Ltd.) and 399.29 g of acetic acid were put into acrystallizing apparatus, dissolved at 95° C. and maintained for 10minutes, and then cooled to 15° C. with stirring. Upon expiration of 55minutes after the temperature became 15° C., 0.5 g of adipic acid(manufactured by Wako Pure Chemical Industries, Ltd.) was added as seedcrystals. The system was left to stand for 3 hours and then subjected tofiltration.

The mother liquor (the filtrate) was 420.5 g, and a solid was recoveredin an amount of 25.65 g. The obtained solid content was analyzed fororganic substances by liquid chromatography and for ammonia by ionchromatography, whereby propionic acid was 35.3 wt %, adipic acid was56.8 wt %, and ammonia was 5.5 wt %. Likewise, the mother liquor wasfound to comprise 90.6 wt % of propionic acid, 6.2 wt % of adipic acidand 2.2 wt % of ammonia.

-   Recovery rate of adipic acid:    (25.65×0.568)/(50.20×150.1/184.2)=0.356 (35.6% recovery)    -   Solid molar composition:

Adipic acid 25.65 × 0.568/150.1 = 0.097 Propionic acid 25.65 × 0.353/74= 0.127 Ammonia 25.65 × 0.055/17 = 0.086

25.2 g of the obtained solid content was dissolved at 95° C. by using99.99 g of propionic acid and then cooled to 15° C. Precipitationstarted immediately. The system was left to stand for 3 hours and 53minutes and then subjected to filtration. The obtained solid was 16.48g, and the mother liquor was 104.4 g. The solid was analyzed, wherebypropionic acid was 28.2 wt %, adipic acid was 69.0 wt % and ammonia was0.4 wt %. Likewise, the mother liquor was found to comprise 94.4 wt % ofpropionic acid, 3.3 wt % of adipic acid and 1.1 wt % of ammonia.

-   Recovery rate of adipic acid: (16.48×0.568)/(25.2×0.690)=0.794    (79.4% recovery)    -   Solid molar composition:

Adipic acid 16.48 × 0.690/150.1 = 0.076 Propionic acid 16.48 × 0.282/74= 0.063 Ammonia 16.48 × 0.004/17 = 0.004

Example 2

Now, a test for distillation of a monocarboxylic acid and an ammoniumsalt of the monocarboxylic acid, will be described.

Preparation of Model Mother Liquors

{circle around (1)} Preparation of Model Mother Liquor 1

The composition of the mother liquor after reactive crystallization willbe influenced by the amount of the solvent in the reactivecrystallization and the purity of the solvent at the time of recyclingand will be determined by the optimum operational condition by such acondition as utility. To see the difference in separation performancebased on the melting point of the ammonium salt of a monocarboxylicacid, as the monocarboxylic acid, acetic acid was selected, which isconsidered to be preferred among those having from 1 to 6 carbon atoms,as disclosed in JP-A-2002-135656. The type of the di/tricarboxylic acidgives no influence on the separation of the monocarboxylic acid and theammonium salt of the monocarboxylic acid, although its influence overthe boiling point slightly differs. In the present Test Examples, as thedi/tricarboxylic acid, succinic acid was selected as a standardsubstance.

The solubility of ammonium succinate in acetic acid was confirmed to besuch that it dissolved up to a concentration of 33 wt % at 100° C. andup to 10 wt % at 16° C. Therefore, on the assumption that thetemperature of industrial water is about 20° C., the crystallizationtemperature was assumed to be from about 30 to 50° C., and it wasassumed that it would remain at a concentration of about 20 wt % in thecrystallization mother liquor after the crystallizing operation.Therefore, assuming a crystallization mother liquor obtained byseparating succinic acid precipitated by reactive crystallization bymeans of acetic acid, about 120 g of acetic acid manufactured by WakoPure Chemical Industries, Ltd. and about 30 g of ammonium succinatemanufactured by Wako Pure Chemical Industries, Ltd. were mixed, heatedand completely dissolved to obtain a solution having an ammoniumsuccinate concentration of about 20 wt %, which was designated as “modelmother liquor 1”. As mentioned above:

Succinic acid primary pKa: 4.21

Succinic acid secondary pKa: 5.64

Acetic acid pKa: 4.76.

Accordingly, it is considered that while this model mother liquor 1comprises:

Charge: Acetic acid 120 g (2 mol)

-   -   Diammonium succinate 30.4 g (0.2 mol, about 20 wt %),        the diammonium succinate is reacted with acetic acid to have        approximately the following composition:

Dissolved liquid: Acetic acid 108 g (1.8 mol)

-   -   Monoammonium succinate 27 g (0.2 mol)    -   Ammonium acetate 15.4 g (0.2 mol)        {circle around (2)} Preparation of Model Mother Liquor

Propionic acid manufactured by Wako Pure Chemical Industries, Ltd.,diammonium succinate manufactured by Wako Pure Chemical Industries, Ltd.and 28% aqueous ammonia manufactured by Wako Pure Chemical Industries,Ltd. were mixed in the following ratio, heated and completely dissolvedto obtain a solution, which was designated as “model mother liquor 2”.

Charge: Propionic acid 98.75 g (1.33 mol)

-   -   Diammonium succinate 20.29 g (0.133 mol)    -   28% aqueous ammonia 13.32 g (0.22 mol: ammonia)

This model mother liquor 2 comprises:

Succinic acid primary pKa: 4.21

Succinic acid secondary pKa: 5.64

Propionic acid pKa: 4.67.

Accordingly, it is considered that the diammonium succinate is reactedwith propionic acid to have approximately the following composition:

Dissolved liquid: Propionic acid 1.2 mol (88.8 g)

-   -   Monoammonium succinate 0.133 mol    -   Ammonium propionate 0.35 mol (0.22 mol+0.133 mol)    -   Water 9.6 g (7.2 wt %)

Distillation Tests Test Example 2-1 The Lower Limit Temperature

Model mother liquor 1 (acetic acid: 120.00 g, diammonium succinate:30.42 g) was prepared, and then this mother liquor was put into a 200 mleggplant type flask, installed in a simple distillation apparatus andsubjected to simple distillation at 10 mmHg. A condenser ofwater-cooling type was employed. A very small amount of nitrogen gas wasconstantly circulated in the simple distillation apparatus for thepurpose of preventing bumping and for the purpose of increasing thedistillation efficiency.

When the temperature in the flask became 36° C., distillation started,and when it became 69° C., no substantial distillate was observed, andthe distillation was terminated. In the flask, precipitation occurredand solidification was observed.

The distilled amount was 40 ml (45.65 g). The amount of the content inthe flask was 64.78 g from deduction of the tare of the flask and thebalance between before and after the test. It is believed that the restwas not sufficiently condensed in the condenser and was released fromthe reduced pressure line to a draft, since the temperature of thecooling water of the condenser was high as compared with the degree ofreduced pressure.

Test Example 2-2 Upper Limit Temperature

Model mother liquor 1 (acetic acid: 120.18 g, diammonium succinate:30.40 g) was prepared, then put into a 200 ml eggplant type flask,installed in a simple distillation apparatus and subjected to simpledistillation at 150 mmHg. A condenser of water cooling type was used. Avery small amount of nitrogen gas was constantly circulated to thesimple distillation apparatus for the purpose of preventing bumping andfor the purpose of increasing the distillation efficiency.

When the temperature in the flask became 85° C., distillation started,and after the temperature of an oil bath became 105° C., distillationwas continued while reducing the pressure by 10 mmHg each time. Uponexpiration of 1 hour and 45 minutes, the distilled amount reached 40 ml.Here, the first distillate sample was recovered. At that time, thetemperature in the flask was 89° C., and the pressure was 120 mmHg.

Thereafter, an operation of reducing the pressure when the distillationstopped, was repeated, so that the temperature of the flask would notexceed 100° C. The temperature of the oil bath was controlled not toexceed the melting point (114° C.) taking into consideration afluctuation or error of the thermometer, and 109° C. was the maximum.Upon expiration of 1 hour and 47 minutes from the first sampling, asample was collected when 40 ml was distilled. At that time, thetemperature in the flask was 95° C., and the pressure was 60 mmHg.

The pressure was returned to atmospheric pressure, 2.55 g of the bottomsample was collected. The amount of the content in the flask was 64.96 gfrom deduction of the tare of the flask and the balance between beforeand after the test. No precipitation of crystals was observed throughoutthe period of the simple distillation.

Test Example 2-3 Excess Temperature

Model mother liquor 1 (acetic acid: 120.03 g, diammonium succinate:30.41 g) was prepared, then put into a 200 ml eggplant type flask,installed in a simple distillation apparatus and subjected to simpledistillation at 380 mmHg. A condenser of water cooling type was used. Avery small amount of nitrogen gas was constantly circulated to thesimple distillation apparatus for the purpose of preventing bumping andfor the purpose of increasing the distillation efficiency.

When the temperature in the flask became 110° C., distillation started,and in about 1 hour, the temperature reached 114° C. Thereafter, thedistillation rate did not increase, and in further 45 minutes, thedistilled amount reached 40 ml (corresponding to Test Example 2-1).Here, the first distillate sample was recovered. At that time, thetemperature was 118° C. When further 40 ml was distilled, (132° C.; uponexpiration of 1 hour and 10 minutes from the first sampling), thepressure was once returned to atmospheric pressure, and the seconddistillate sample and 2.55 g of the bottom sample were collected. Thepressure was again reduced to 380 mmHg, and when 2.97 g was distilled,the distillation was terminated. The amount of the content in the flaskwas 54.47 g from deduction of the tare of the flask and the balancebetween before and after the test. No precipitation of crystals wasobserved throughout the period of the simple distillation.

Test Example 2-4 Effect of Water

In the same manner as for model mother liquor 1, 30.40 g of succinicacid was used. Instead of 120 g of acetic acid in model mother liquor 1,72.02 g of acetic acid and 48.01 g of water were used to dissolve thesuccinic acid.

The solution was put into a 200 ml eggplant type flask, installed in asimple distillation apparatus and subjected to simple distillation atatmospheric pressure. A condenser of water cooling type was used. A verysmall amount of nitrogen gas was constantly circulated to the simpledistillation apparatus for the purpose of preventing bumping and for thepurpose of increasing the distillation efficiency.

When the temperature in the flask became 132° C. (oil bath temperature:158° C.), distillation started, and in 20 minutes, 40 ml (42.64 g) wasdistilled, and a sample was collected. Further, over a period of 34minutes, 40 ml (41.88 g) was distilled (the temperature in the flask:150° C., oil bath: 180° C.), and a sample was collected. At that time,from the bottom, 2.71 g was sampled. Further, heating was continued, andwhen 20 ml (22.08 g) was distilled (the temperature in the flask: 169°C., oil bath: 206° C.), the distillation was terminated, and thedistillate and the bottom were, respectively, sampled. The bottom was39.27 g from deduction of the tare of the flask and the balance betweenbefore and after the test.

Test Example 2-5 In the Case of Propionic Acid

Model mother liquor 2 was put into a 200 ml eggplant type flask andinstalled in a simple distillation apparatus. After reducing thepressure to 100 mmHg, heating was initiated. A condenser of watercooling type was used. A very small amount of nitrogen gas wasconstantly circulated to the simple distillation apparatus for thepurpose of preventing bumping and for the purpose of increasing thedistillation efficiency.

When the temperature in the flask became 72° C., distillation started.When the temperature in the flask became 83° C., the pressure wasreduced to maintain the temperature, and thus the pressure was reducedto 50 mmHg. Subsequently, when the temperature became 90° C. and uponexpiration of 55 minutes from the initiation of the distillation, thedistillate was sampled. At the at that time, the temperature of the oilbath was 100° C. Upon expiration of 1 hour from the initiation of thedistillation, distillation was continued for 20 minutes by raising thetemperature to 105° C. and further for 20 minutes by raising thetemperature to 108° C., whereupon the bottom and the distillate weresampled. The temperature in the flask upon completion of thedistillation was 95° C.

The first distillate recovered was 37.0 g, the second distillate was15.25 g, and the bottom was 79.7 g.

In Test Example 2-5, on the same basis as for the analysis, i.e. on theassumption that the acid and the base are separately present, the chargecomprised:

Propionic acid 98.75 g Ammonia 20.29 × 34/152 + 13.32 × 0.28 = 8.27 gSuccinic acid 20.29 × 118/152 + 15.75 g Water 13.32 × 0.72 = 9.59 g.

Test Example 2-6 The Minimum Temperature for Vaporization of AmmoniumAcetate

Taking into consideration, the results of Test Examples 2-1 and 2-2,vaporization of ammonium acetate in an acetic acid-succinic acid systemwas investigated by means of the following model solution.

29.99 g of acetic acid, 15.19 g of ammonium succinate and further 7.69 gof ammonium acetate in order to more accurately grasp the vaporizationof ammonium acetate, were put into a 200 ml eggplant type flask andinstalled in a rotary evaporator. The pressure was reduced to 30 mmHg,and the flask was immersed in an oil bath heated to 108° C. and heatedfor 27 minutes.

At a condenser portion, white solid was precipitated and deposited. Thebottom was white solid which was precipitated and solidified, and itsamount was 27.93 g.

On the same basis as for the analysis, i.e. on the assumption that theacid and the base are present separately, the charge comprised:

Acetic acid 29.99 + 7.69 × 60/77 = 35.98 g Ammonia 15.19 × 34/152 + 7.69× 17/77 = 5.10 g Succinic acid 15.19 × 118/152 = 11.79 g.

Test Example 2-7 Maximum Temperature for Vaporization of AmmoniumAcetate

On the basis of the results of Test Examples 2-1 and 2-2 and further inconsideration of an idea that it may be advantageous to add water undera high temperature condition in view of Test Examples 2-3 and 2-4,vaporization of ammonium acetate in an acetic acid-succinic acid systemwas investigated by means of the following model solution.

24.00 g of acetic acid, 15.20 g of ammonium succinate, 6.11 g ofdeionized water and further 7.68 g of ammonium acetate in order to moreaccurately grasp the vaporization of ammonium acetate, were put into a200 ml eggplant type flask and installed in a rotary evaporator. Thepressure was reduced to 150 mmHg, and the flask was immersed in an oilbath heated to 150° C., whereupon the oil bath was heated to 178° C. Thedistillation rate became slow immediately, but in consideration ofcomparison to Test Example 2-6, heating was continued for 30 minutes.

At a condenser portion, white solid was precipitated and deposited. Thebottom was white solid which was precipitated and solidified, and itsamount was 16.07 g.

On the same basis as for the analysis, i.e. on the assumption that theacid and the base are present separately, the charge comprised:

Acetic acid 24.00 + 7.68 × 60/77 = 35.98 g Ammonia 15.20 × 34/152 + 7.68× 17/77 = 5.10 g Succinic acid 15.20 × 118/152 = 11.80 g.

Test Example 2-8

30.00 g of acetic acid, 15.18 g of ammonium succinate and further, 7.71g of ammonium acetate in order to more accurately grasp the vaporizationof ammonium acetate, were put into a 200 ml eggplant type flask andinstalled in a rotary evaporator. The pressure was reduced to 50 mmHg,and the flask was immersed in an oil bath heated to 100° C. When thetemperature of the oil bath became 132° C., distillation started, and 25minutes later, the bottom underwent precipitation and solidification at139° C., and the distillation was terminated. The amount of the bottomwas 22.71 g. At a condenser portion, white solid was precipitated anddeposited.

On the same basis as for the analysis, i.e. on the assumption that theacid and the base are separately present, the charge comprised:

Acetic acid 30.00 + 7.71 × 60/77 = 36.01 g Ammonia 15.18 × 34/152 + 7.71× 17/77 = 5.10 g Succinic acid 15.18 × 118/152 = 11.78 g.

Test Example 2-9 Effects of Water

On the basis of the results of Test Examples 2-1 and 2-2 and inconsideration of an idea that it may be advantageous to add water inview of Test Example 2-3 and 2-4, the vaporization of ammonium acetatein an acetic acid-succinic acid system was investigated by means of thefollowing model solution on the assumption that water is added or to beadded to the crystallization solvent.

7.50 g of acetic acid, 15.23 g of ammonium succinate, 35.99 g ofdeionized water and further, 7.68 g of ammonium acetate in order to moreaccurately grasp the vaporization of ammonium acetate, were put into a200 ml eggplant type flask and installed in a rotary evaporator. Thepressure was reduced to 50 mmHg, and the flask was immersed in an oilbath heated to 137° C. During the test, the temperature of the oil bathchanged within a range of from 137 to 138° C.

The distillation was complete in 17 minutes, and the bottom was whitesolid which was precipitated and solidified, and its amount was 27.96 g.At a condenser portion, white solid was precipitated and deposited.

On the same basis as for the analysis, i.e. on the assumption that theacid and the base are separately present, the charge comprised:

Acetic acid 7.50 + 7.68 × 60/77 = 13.48 g Ammonia 15.23 × 34/152 + 7.68× 17/77 = 5.10 g Succinic acid 15.23 × 118/152 = 11.82 g.

Test Example 2-10 Vaporization of Ammonium Propionate

Ammonium propionate is not commercially available. Therefore, 39.99 g ofpropionic acid, 15.23 g of ammonium succinate and 15.16 g of 28% aqueousammonia manufactured by Wako Pure Chemical Industries, Ltd. were used asa model solution.

This model solution was put into an eggplant type flask and installed ina rotary evaporator. The pressure was reduced to 40 mmHg, and the flaskwas immersed in an oil bath heated to 157° C. The temperature was 160°C. during the test. In this state, distillation was carried out for 25minutes.

At a condenser portion, white solid was precipitated and deposited. Thebottom was white solid which was precipitated and solidified, and itsamount was 25.38 g.

On the same basis as for the analysis, i.e. on the assumption that acidand base are separately present, the charge comprised:

Propionic acid 39.99 g Ammonia 15.20 × 34/152 + 15.16 × 0.28 = 3.41 gSuccinic acid 15.23 × 118/152 = 11.82 g.

Results

The results of the foregoing distillation tests are shown in Tables 2-1to 2-4.

TABLE 2-1 Simple distillation: Corresponding to a kettle type evaporatorMaximum Maximum temp. liquid in the temp. Charged oil in the aceticCharged Charged Charged Pressure bath flask Overall acid ammoniasuccinic water (mmHg) (° C.) (° C.) time (g) (g) acid (g) (g) Ex. 1Distillate  10 77 69 2 hr Bottom  10 77 69 2 hr Balance 120.00 6.8023.62 0.00 Ex. 2 Distillate 1 150-60 105 89 1 hr 45 min Distillate 2150-60 109 95 3 hr 19 min Bottom 150-60 109 95 3 hr 19 min Balance120.18 6.80 23.60 0.00 Ex. 3 Distillate 1 380 134 118 1 hr 40 minDistillate 2 380 149 132 3 hr 47 min Bottom 1 380 149 132 3 hr 47 minBottom 2 380 160 132 4 hr 25 min Balance 120.03 6.80 23.61 0.00(bottom 1) Ex. 4 Distillate 1 760 142 116 53 min Distillate 2 760 160139 2 hr 36 min Distillate 3 760 175 156 3 hr 48 min Bottom 1 760 160139 2 hr 36 min Bottom 2 760 175 156 3 hr 48 min Balance 72.02 6.8023.60 48.01 (bottom 1) Ex. 5 Distillate 1 100-50 97-100 72-90 55 minDistillate 2 100-50 100-108  90-95 1 hr 40 min Bottom 100-50 97-10872-95 1 hr 40 min Balance *98.75 8.27 15.75 9.59 *Propionic acid

TABLE 2-2 Simple distillation: Corresponding to a kettle type evaporatorAcetic Total Ammonia acid Ammonia Succinic Amide Amidated Distilled in(g) (g) acid (g) (g) ammonia ammonia bottle 1 Ex. 1 Distillate 46.690.03 0.00 0.00 Bottom 33.87 6.71 23.14 0.00 0.00 0.00 0.39 mol Balance80.56** 6.73 23.14 0.00 0.00 0.00 1.00 mol fraction Ex. 2 Distillate 142.14 0.15 0.00 0.00 Distillate 2 42.76 0.05 0.00 0.00 Bottom 34.97 6.3521.99 1.21 0.01 0.01 0.37 mol Balance 119.88 6.54 21.99 1.21 0.03 0.030.94 mol fraction Ex. 3 Distillate 1 41.72 0.05 0.00 0.00 Distillate 240.36 0.01 0.00 0.00 Bottom 1 29.58 3.67 10.81 11.88 0.11 0.00 0.22 molBottom 2 25.32 2.99 8.57 13.07 0.32 0.01 0.66 mol fraction Balance111.66 3.74 10.81 11.88 (bottom 1) Ex. 4 Distillate 1 16.48 0.01 0.000.00 Distillate 2 21.47 0.02 0.00 0.00 Distillate 3 11.28 0.05 0.00 0.00Bottom 1 31.90 4.52 14.67 9.30 0.08 0.00 0.27 mol Bottom 2 14.66 1.665.69 15.58 0.23 0.01 0.75 mol fraction Balance 69.86 4.56 14.67 9.30(bottom 1) Ex. 5 Distillate 1 *26.20 0.28 0.00 0.00 Distillate 2 13.700.56 0.00 0.00 Bottom 54.29 7.34 14.50 0.20 0.00 0.05 0.43 mol Balance94.19 8.18 14.50 0.20 0.00 0.10 0.89 mol fraction *Propionic acid**(Partly leaked without being condensed)

TABLE 2-3 Rotary evaporator: Corresponding to a thin film typeevaporator Maximum Maximum temp. liquid in the temp. Charged oil in theacetic Charged Charged Charged Pressure bath flask Overall acid ammoniasuccinic water (mmHg) (° C.) (° C.) time (g) (g) acid (g) (g) Ex. 6Distillate 30 108-110 UM 27 min Bottom 30 108-110 UM 27 min Balance35.98 5.10 11.79 0.00 Ex. 7 Distillate 150 150-178 UM 30 min Bottom 150150-178 UM 30 min Balance 29.98 5.10 11.80 6.11 Ex. 8 Distillate 50132-139 UM 25 min Bottom 50 132-139 UM 25 min Balance 36.01 5.10 11.780.00 Ex. 9 Distillate 50 137-138 UM 17 min Bottom 50 137-138 UM 17 minBalance 13.48 5.10 11.82 35.99 Ex. 10 Distillate 40 157-160 UM 25 minBottom 40 157-160 UM 25 min Balance *39.99 3.41 11.82 0.00 UM:Unmeasurable *Propionic acid

TABLE 2-4 Rotary evaporator: Corresponding to a thin film typeevaporator Acetic Total Ammonia acid Ammonia Succinic Amide AmidatedDistilled in (g) (g) acid (g) (g) ammonia ammonia bottle Ex. 6Distillate 4.32 0.08 0.00 0.00 (Calculated value) Bottom 12.68 3.5011.69 0.07 0.0006 0.09 0.21 mol Balance 17.00*** 3.59 11.69 0.07 0.000.31 0.69 mol fraction Ex. 7 Distillate 15.05 1.45 0.00 0.00 (Calculatedvalue) Bottom 2.37 1.52 9.56 2.28 0.0197 0.19 0.09 mol Balance 17.43***2.98 9.56 2.28 0.07 0.64 0.30 mol fraction Ex. 8 Distillate 5.64 0.140.00 0.00 (Calculated value) Bottom 7.60 2.88 12.25 0.16 0.0014 0.130.17 mol Balance 14.44*** 3.02 12.25 0.16 0.00 0.43 0.57 mol fractionEx. 9 Distillate 0.51 0.04 0.00 0.00 (Calculated value) Bottom 10.394.28 11.79 0.00 0.0000 0.05 0.25 mol Balance 10.90*** 4.32 11.79 0.000.00 0.16 0.84 mol fraction Ex. 10 Distillate *13.60 2.54 0.00 0.00(Calculated value) Bottom 2.77 1.30 10.45 1.20 0.0103 0.11 0.08 molBalance 16.37*** 3.84 10.45 1.20 0.05 0.57 0.38 mol fraction *Propionicacid ***(Solid precipitated in the condenser)

Discussion

In a succinic acid-acetic acid system, an ammonium salt of acid B ismeant for ammonium acetate, and its melting point is known to be 114° C.In Test Example 2-3, the oil bath was from 134° C. to 149° C., and theliquid temperature in the flask exceeded 114° C., and the maximum was132° C. The elapsed time was about 2 hours. At that time, acetamide wasformed as much as 7.4 wt %, and further, succinic acid amide, etc. wereformed. Succinic acid introduced, was 30.4 g (corresponding to 0.2 mol)as ammonium succinate, and succinic acid remaining in the bottomdecreased to a level of 0.09 mol. Whereas, in Test Example 2-2, thetemperature of the oil bath i.e. the wall temperature of the flask was109° C., the liquid temperature in the flask was 95° C., and the elapsedtime was as much as 3.3 hours. Nevertheless, acetamide was formed onlyat a level of 0.4 wt %, and likewise, succinic acid was 30.4 g(corresponding to 0.2 mol) as ammonium succinate, and it corresponds to0.186 mol in such a state that it is not detected in the distillate.Thus, the difference is distinct.

From such results, the present inventor considered that there must be atemperature which is specifically influential over the reaction foramidation of ammonium carboxylate at a level of around 120° C. as anaverage temperature during the operation, which is higher than theliquid temperature of 95° C. in Test Example 2-2 and which is not higherthan the liquid temperature of 132° C. in Test Example 2-3.

The melting point of ammonium acetate is 114° C., and as mentionedabove, the melting point of ammonium propionate is considered to beabout 100° C.

In these tests, the operation temperature is assumed to be about themelting point or slightly higher than the melting point. Accordingly,especially in the distillate 2, it is considered that ammonia isslightly evaporated by pyrolysis. However, during the majority of theelapsed time, the temperature in the flask is not higher than 95° C.,amidation is observed to be not extremely advanced. In the case ofacetic acid in Test Example 2-2, the retention time exceeded 3 hours,and the temperature was at least 90° C. for about 1 hour and a half. Inthe case of Test Example 2-5, taking into consideration the retention ofabout 40 minutes, the amidation ratio may be regarded as substantiallythe same within a range of analytical error.

It is important that acetic acid or propionic acid as acid B is takenout in a state where it contains no ammonia, and organic acid A and itsammonium salt are concentrated while avoiding amidation or imidation.For such a purpose, it is necessary to take as a threshold whichever islower, about 110° C. as the reaction singular point or the melting pointof acid B. Accordingly, in the case of acetic acid, the reactionsingular point is unclear in a strict sense and substantially the sametemperature as the melting point, and accordingly, an operationalcondition is adjusted at a temperature not higher than 114° C. as themelting point of acetic acid. In the case of propionic acid, the meltingpoint of propionic acid is unclear, and in the Test Example, theevaporated amount of ammonia is not higher than 1/10 of the chargedamount in spite of such a long retention time as 1 hour and 40 minutes,and such is considered to be practically within an allowable range, andtherefore, a temperature of the level in this Test Example is consideredto be the upper limit temperature. Namely, it is 110° C. inconsideration of the temperature of the wall surface (the temperature ofthe oil bath). The temperature of the wall surface is not usuallymeasured, and therefore, 110° C. as the temperature of the utility to beused for heating will be the upper limit. This corresponds to a liquidtemperature of 100° C., which may be considered as corresponding to themelting point of ammonium propionate. Accordingly, in the case wherepropionic acid is employed, the temperature of the process fluid beingat most 100° C. will be the operational condition. It is only requiredthat the operational condition of either the utility or the processfluid is satisfied.

Further, as Comparative Examples, Test Examples 2-3 and 2-4 were carriedout. This is based on an idea that the amidation or imidation reactionmay be suppressed when water is contained. Under the conditions of TestExamples 2-1 and 2-2, amidation or imidation is slight, and nosignificant difference can be observed within a range of analyticalerror. Accordingly, the investigation is made intentionally under acondition where amidation or imidation takes place. From the results, asignificant difference is distinctly observed. Thus, it can be said thatit is advisable that water is present to some extent during thevaporization of acid B.

In a test on a method of vaporizing an ammonium salt of acid B aftervaporization of acid B from the crystallization mother liquor, notnegligible is the retention time. As mentioned above, the reaction foramidation becomes rapid at a temperature of about 120° C. On the otherhand, a higher temperature is required to separate the ammonium salt ofacid B from organic acid A and its ammonium salt, since a temperature ofat least the melting point of the ammonium salt of acid B is ideal.

In the case of a simple distillation apparatus, a connecting portionfrom the flask as the heating portion to a condenser portion, is exposedto the outside air, whereby the outside air and the process undergo heatexchange to cause an internal reflux. Consequently, unless thedifference between the heat release at the connecting portion and theheating at the flask portion is substantially large, the retention timeincreases. In Test Example 2-3, the temperature of the oil bath wasrapidly raised, and the heating calorie was large. Nevertheless, theretention time was long, because the temperature difference between theprocess and the outside air became also large, and the heat release atthe connecting portion became likewise large.

Therefore, the present inventor conducted a test in which a rotaryevaporator was used. In the rotary evaporator, the flask is installedobliquely to the oil bath and is rotated so that the flask can beuniformly heated to a portion close to the connecting portion. Besides,a portion from the connecting portion of the flask to the condenser isshielded from the outside air by a driving portion, whereby heatexchange with the outside air is substantially minimized. As a result,the internal reflux is minimum, and the retention time can be shortened.

However, the liquid temperature in the rotating flask can not bemeasured. Namely, in order to shorten the retention time, the amount ofcharge is intentionally reduced as compared with the size of the flask,whereby even if a thermometer may be inserted, the liquid temperaturecan not be constantly measured, since the liquid surface is always inthe vicinity of the inner wall of the flask. Further, the flask is inrotation, and at the final stage of evaporation, organic acid A and itsammonium salt will solidify, whereby it is difficult to measure thetemperature in the flask.

The ammonium salt of acid B undergoes pyrolysis, whereby it is difficultto measure the physical property such as the boiling point accurately.However, the present inventor considered that theoretically, a boilingpoint is necessarily present, and a phenomenon such as sublimation takesplace, whereby it may simply be that one due to pyrolysis can not bedistinguished from the contribution of vaporization or sublimation.Therefore, a test was carried out in which the ammonium salt of acid Bwas evaporated in a reduced pressure system by shortening the retentiontime. Test Examples 2-6, 2-7 and 2-8 are tests in which a rotaryevaporator was used.

In Test Example 2-6, it has been found that by sufficiently reducing thepressure and using an oil bath i.e. a heat source of about 110° C.,ammonium acetate can be vaporized. This is a phenomenon at a temperatureof not higher than the melting point, and it is assumed that sublimationtook place. In Test Example 2-7, ammonium acetate was adequatelyvaporized even under a relatively mild reduced pressure condition at alevel of 150 mmHg. In a practical process, the retention time can beshortened, and it has been proved that a design can be made under thiscondition. However, in this test, for the purpose of comparison, theretention time was prolonged to correspond to Test Example 2-6 while theoil bath i.e. the heat source was set at 180° C., whereby amidation tookplace to some extent. This indicates that if the temperature of the heatsource is made high, the retention time must be shortenedcorrespondingly.

In Test Example 2-9, water evaporated quickly, whereby it was difficultto determine the factor for the suppression of amidation i.e. whether itwas due to a short time or it was due to suppression of dehydrationreaction by the presence of water. However, it has been confirmed thatboth effects contributed substantially and that amidation can be loweredby the presence of water.

Accordingly, as a method for vaporizing acid B after concentrating thecrystallization mother liquor, one having a short heating time ispreferred. Further, it is preferred to vaporize under a superheatedstate i.e. to heat the process fluid under a reduced pressure conditionby a sufficiently high temperature heat source.

Example 3 Test Example 3-1 Test to Confirm the Presence of AmmoniumAcetate (Separation by a Rotary Evaporator)

6.0 g of acetic acid manufactured by Wako Pure Chemical Industries,Ltd., 15.18 g of ammonium succinate manufactured by Wako Pure ChemicalIndustries, Ltd. and 20 g of water were put into a 200 ml eggplant typeflask and installed in a rotary evaporator. The pressure was reduced to50 mmHg, and the flask was heated by immersing it in an oil bath heatedto 140° C. The distillation time was 5 minutes. At a condenser portion,white solid was precipitated and deposited. The bottom was 20.8 g. Thecomposition of this solid was 56.1 wt % (0.099 mol) of succinic acid,19.6 wt % (0.068 mol) of acetic acid and 15.4 wt % (0.189 mol) ofammonia.

Test Example 3-2 Reactive Crystallization

Using a 100 ml reagent bottle, 4.5 g (0.03 mol) of diammonium succinatewas mixed with 30 g (0.5 mol) of acetic acid under heating and dissolvedat 80° C. This solution was left to stand at room temperature (17° C.)for 2 hours. White solid precipitated, and this solid was collected byfiltration. The recovered solid was 1.92 g, and as a result of theanalysis, it was confirmed to comprise 96 wt % of acetic acid and 1 wt %of ammonia.

Test Example 3-3 Gas/Liquid Separation and Concentration afterCrystallization

120 g of acetic acid manufactured by Wako Pure Chemical Industries, Ltd.and 30 g of ammonium succinate manufactured by Wako Pure ChemicalIndustries, Ltd. were mixed, heated and completely dissolved to obtain asolution, which was designated as a crystallization mother liquor.Further,

Succinic acid primary pKa: 4.21

Succinic acid secondary pKa: 5.64

Acetic acid pKa: 4.76.

Accordingly, it is considered that while

Charge: Acetic acid 120 g 2 mol

-   -   Diammonium succinate 30.4 g 0.2 mol (about 20 wt %), the        diammonium succinate is reacted with acetic acid to form        approximately the following composition (as ammonia: 2 wt %).

Dissolved liquid:

Acetic acid  108 g 1.8 mol Monoammonium succinate   27 g 0.2 molAmmonium acetate 15.4 g 0.2 mol

This solution was put into a 200 ml eggplant type flask, installed in asimple distillation apparatus and subjected to simple distillation at150 mmHg. A condenser of water cooling type was used. A very smallamount of nitrogen gas was constantly circulated to the simpledistillation apparatus for the purpose of preventing bumping and for thepurpose of increasing the distillation efficiency.

When the temperature in the flask became 85° C., distillation started,and after the temperature of the oil bath became 105° C., distillationwas carried out while reducing the pressure by 10 mmHg each time. For 1hour and 45 minutes, the distilled amount became 40 ml. Here, the firstdistillate sample was recovered. The temperature in the flask at thattime was 89° C., and the pressure was 120 mmHg.

Thereafter, an operation of reducing the pressure when the distillationstopped, was repeated so that the temperature in the flask would notexceed 100° C. The operation was carried out so that the temperature ofthe oil bath would not exceed the melting point (114° C.) taking intoconsideration a fluctuation or error of the thermometer, and 109° C. wasthe maximum. Over a period of 1 hour and 34 minutes from the firstsampling (overall time: 3 hours and 19 minutes), 40 ml was distilled,whereupon a sample was collected. The temperature in the flask at thattime was 95° C., and the pressure was 60 mmHg.

The pressure was returned to atmospheric pressure, and the bottom samplewas collected. The amount of the content of the flask was 64.96 g fromdeduction of the tare of the flask and the balance between before andafter the test. No precipitation of crystals was observed throughout theperiod of the simple distillation.

In the composition of the first distillate, acetic is acid was 102%(exceeded 100% due to an analytical error); in the composition of thesecond distillate, acetic acid was 103% (exceeded 100% due to ananalytical error), and in the composition of the final bottom, aceticacid was 54%, acetamide 0.4%, succinic acid 34%, succinic acid monoamide1.8%, and ammonia 9.8%.

Test Example 3-4 Gas/Liquid or Gas/Solid Separation to Obtain aDi/Tricarboxylic Acid and its Ammonium Salt

Vaporization of ammonium acetate in an acetic acid-succinic acid systemwas investigated by means of the following model solution.

30.00 g of acetic acid manufactured by Wako Pure Chemical Industries,Ltd., 15.18 g of ammonium succinate manufactured by Wako Pure ChemicalIndustries, Ltd. and further 7.71 g of ammonium acetate in order to moreaccurately grasp the vaporization of ammonium acetate manufactured byWako Pure Chemical Industries, Ltd., were put into a 200 ml eggplanttype flask, and installed in a rotary evaporator. The pressure wasreduced to 50 mmHg, and the flask was immersed in an oil bath heated to100° C., whereupon the oil bath was heated to 140° C. When the oil bathreached 132° C., distillation started. The distillation time was 17minutes.

At a condenser portion, white solid was precipitated and deposited. Thebottom was 22.71 g.

The composition of the bottom was 34% of acetic acid, 0.3% of acetamide,54% of succinic acid, 0.7% of succinic acid monoamide and 12.7% ofammonia.

Test Example 3-5 Conditions for Amidation

120 g of acetic acid manufactured by Wako Pure Chemical Industries, Ltd.and 30 g of ammonium succinate manufactured by Wako Pure ChemicalIndustries, Ltd. were mixed, heated and completely dissolved to obtain asolution, which was designated as a crystallization mother liquor.Further,

Succinic acid primary pKa: 4.21

Succinic acid secondary pKa: 5.64

Acetic acid pKa: 4.76. Accordingly, it is considered that while

Charge: Acetic acid 120 g 2 mol

-   -   Diammonium succinate 30.4 g 0.2 mol (about 20 wt %), the        diammonium succinate is reacted with acetic acid to form        approximately the following composition:

Dissolved liquid:

Acetic acid  108 g 1.8 mol Monoammonium succinate   27 g 0.2 molAmmonium acetate 15.4 g 0.2 mol

This solution was put into a 200 ml eggplant type flask, installed in asimple distillation apparatus and subjected to simple distillation at380 mmHg. A condenser of water cooling type was used. A very smallamount of nitrogen gas was constantly circulated to the simpledistillation apparatus for the purpose of preventing bumping and for thepurpose of increasing the distillation efficiency.

When the temperature in the flask reached 110° C., the first one dropwas distilled, but thereafter, due to internal reflux by heat release,the distillation decreased remarkably. Over a period of 1 hour and 40minutes from the first one drop, the distilled amount became 40 ml(which corresponds to Test Example 3-1). Here, a first distillate samplewas recovered. The temperature at that time was 118° C. When further 40ml was distilled (132° C.; overall time: 3 hours and 47 minutes), thepressure was once returned to atmospheric pressure, whereupon a seconddistillate sample and 2.55 g of a bottom sample were collected. Further,the pressure was reduced to 380 mmHg once again, and when 2.97 g wasdistilled, the distillation was terminated. The amount of the content inthe flask was 54.47 g from deduction of the tare of the flask and thebalance between before and after the test. No precipitation of crystalswas observed throughout the period of the simple distillation.

In the composition of the first distillate, acetic acid was 100%; in thecomposition of the second distillate, acetic acid was 97% (substantially100% within an error range), and in the composition of the bottom at thetime of sampling the second distillate, was 49% of acetic acid, 7.3% ofacetamide, 18% of succinic acid, 16% of succinic acid monoamide and 6.1%of ammonia.

Example 4

In the following, for ammonium acetate, sodium acetate and potassiumacetate, high grade reagents manufactured by Wako Pure ChemicalIndustries, Ltd. were used.

Test Example 4-1

15.22 g (0.198 mol) of ammonium acetate, 20.01 g of deionized water and5.20 g of 28% aqueous ammonia, manufactured by Wako Pure ChemicalIndustries, Ltd. (0.086 mol as ammonia) were put into a 200 ml flask andinstalled in a simple distillation apparatus. The pressure was reducedto 150 mmHg, and the flask was immersed in an oil bath heated to 90° C.When the liquid temperature in the flask became 62° C., distillationstarted. When the liquid temperature in the flask became 75° C., thedistillate was sampled. The distillate was sampled. The amount was 15.79g. Then, the pressure was reduced to 100 mmHg, to obtain 3.35 g of adistillate and 18.54 g of a bottom.

Acetic acid contained in the first distillate was 0.34 wt %, the aceticacid contained in the second distillate was 0.72 wt %, and acetic acidcontained in the bottom was 62.4 wt % (0.193 mol). Ammonia in the bottomwas 13.9 wt % (0.152 mol).

From this result, it has been proved that acetic acid is present in theform of ammonium acetate, which is not substantially vaporized at atemperature of not higher than the melting point (114° C.) of ammoniumacetate, whereby aqueous ammonia can be separated.

Test Example 4-2

A test was carried out by a test apparatus shown in FIG. 6.

As a distillation column 10, an Oldarshow distillation column having 20plates, was used. In order to improve the liquid hold and thedistillation efficiency, an inert gas from a steel bottle 11 wascirculated to this distillation column 10 via column bottom flask 13immersed in an oil bath 12, and a non-condensed gas was discharged intoa draft from a gas purge line 15 via a condenser 14.

The charge was 249.9 g of ammonium acetate, 150.0 g of sodium acetateand 250.0 g of deionized water and was preliminarily heated to 90° C. ina feed material tank 16 equipped with a temperature-keeping means. Thecapacity of the flask 13 at the column bottom was 500 ml, and forstartup, 30.06 g of ammonium acetate, 20.27 g of sodium acetate and70.16 g of acetic acid were charged.

When the inner temperature of the column bottom flask 13 became 120° C.,the feed material in the feed material tank 16 was supplied at a flowrate of 165 cc/hr from the top of the distillation column 10 via apreheater 17. At that time, the temperature of the preheater 17 was 110°C.

After an operation for 51 minutes from the initiation of the supply ofthe feed material, 63.6 g of the distillate and 120.5 g of the bottom inthe flask were withdrawn as the first withdrawal. After an operation forfurther 37 minutes, 43.9 g of the distillate and 71.1 g of the bottom inthe flask were withdrawn as the second withdrawal.

Thereafter, a steady state was assumed.

Further, after an operation for 36 minutes, 44.5 g of the distillate and60.3 g of the bottom in the flask were taken out as the first analyticalsamples. After an operation for further 36 hours, 46.3 g of thedistillate and 74.5 g of the bottom in the flask were taken out as thesecond analytical samples.

The compositions of the respective analytical samples were as shown inTable 4-1.

TABLE 4-1 Composition (wt %) Analytical Acetic samples acid AmmoniaAcetamide Na Water First Distillate 0.5 7.9 Rest (44.5 g) Bottom 71.83.8 9.1 9.9 5.4 (60.3 g) (calculated value) Second Distillate 0.5 8.2Rest (46.3 g) Bottom 72.6 4.0 8.1 10.1 5.2 (74.5 g) (calculated value)

As is apparent from Table 4-1, there is no substantial difference in thecomposition between the first and second analytical samples, and thus,the operation can be regarded as substantially steady. On the basis thatthe operation was substantially in a steady state, if the composition ofthe supplied feed material and the composition of the second analyticalsamples are compared, the mass balance will be as shown in the followingTable 4-2. Here, the supplied material of 165 cc/hr was converted to aunit of g/hr by using the specific gravity of the feed material being1.14.

Further, the amount of the acetamidated ammonia was obtained bycalculation as follows. Namely, as shown in Table 4-1, acetamide in thebottom was 8.1 wt %, which was calculated as ammonia by molar amount,which is then converted to a weight amount to obtain 1.7 g.

TABLE 4-2 Distillate Bottom (excluding (withdrawn non- from the Suppliedcondensed column amount gas) bottom) Acetamidated Components (g/hr)(g/hr) (g/hr) ammonia Acetic 50.3 0.2 54.1 — acid Water 43.9 42.3 3.9 —Ammonia 9.7 3.8 3.0 1.7 Na 7.4 0.0 7.5 —

As is apparent from Table 4-2, the total of the analytical values ofammonia is 8.5 g/hr (=3.8+3.0+1.7), which is substantially differentfrom the supplied amount of 9.7 g/hr, and the difference is remarkableas compared with other substances. This is attributable mainly to thefact that a part of ammonia was lost into a draft together with anon-condensed gas, and it was evaporated during the sampling or duringthe preparation of the standard solution for the analysis.

When it is considered that ammonium acetate and acetamide remaining inthe bottom (withdrawn from the column bottom) were not decomposed anddistilled, it is apparent that 51.3% of ammonia supplied as ammoniumacetate was distilled off or separated as a non-condensed gas, and atthe same time, it was possible to obtain acetic acid having anunbelievably low water content and aqueous ammonia containing no aceticacid, by a distillation column having only 20 plates.

Test Example 4-3

Using the test apparatus as shown in FIG. 6, a test was carried out inthe same manner as in Test Example 4-2 except that as the feed material,ammonium acetate, sodium acetate and potassium acetate were used, andthe amount of the charge of the feed material and the operationconditions were changed.

The charge was 250 g of ammonium acetate, 150.0 g of potassium acetateand 250.0 g of deionized water, and it was preheated to 90° C. To thecolumn bottom flask, for startup, 30.04 g of ammonium acetate, 20.28 gof potassium acetate and 70.27 g of acetic acid were charged.

When the internal temperature of the column bottom flask became 120° C.,the feed material was supplied from the column top at a flow rate of 150cc/hr. At that time, the temperature of the preheater was 110° C.

After an operation for 59 minutes from the initiation of the supply ofthe feed material, 65.7 g of the distillate and 133.4 g of the bottom inthe flask were taken out as the first withdrawal. After an operation forfurther 40 minutes, 43.5 g of the distillate and 76.2 g of the bottom inthe flask were taken out as the second withdrawal.

Thereafter, a steady state was assumed.

Further, after an operation for 40 minutes, 42.6 g of the distillate and68.5 g of the bottom in the flask were taken out as the first analyticalsamples. After an operation for further 40 minutes, 43.5 g of thedistillate and 68.1 g of the bottom in the flask were taken out as thesecond analytical samples.

The compositions of the respective analytical samples were as shown inTable 4-3.

TABLE 4-3 Composition (wt %) Analytical Acetic samples acid AmmoniaAcetamide K Water First Distillate 0.3 7.1 Rest (42.6 g) Bottom 69.6 2.15.3 17.7 5.5 (68.5 g) (calculated value) Second Distillate 0.3 8.7 Rest(43.5 g) Bottom 68.3 2.1 5.0 17.5 7.1 (68.1 g) (calculated value)

As is apparent from Table 4-3, there is no substantial difference in thecomposition between the first and second analytical samples, and theoperation can be regarded as substantially steady. On the basis that theoperation is substantially in a steady state, if the composition of thesupplied feed material and the composition of the second analyticalsamples are compared, the mass balance will be as shown in the followingTable 4-4. Here, the supplied material of 150 cc/hr was converted to aunit of g/hr by using the specific gravity of the feed material being1.14.

Further, the amount of the acetamidated ammonia was obtained bycalculation as follows. Namely, as shown in Table 4-3, acetamide in thebottom was 5.0 wt %, which was calculated as ammonia by molar amount,which was converted to a weight to obtain 1.0 g.

TABLE 4-4 Distillate Bottom (excluding (withdrawn non- from the Suppliedcondensed column amount gas) bottom) Acetamidated Components (g/hr)(g/hr) (g/hr) ammonia Acetic 50.6 0.1 46.5 — acid Water 44.2 39.7 4.8 —Ammonia 9.7 3.8 1.4 1.0 K 8.0 0.0 11.9 —

As is apparent from Table 4-4, the total of the analytical values ofammonia is 6.2 g/hr (=3.8+1.4+1.0), which is substantially differentfrom the supplied amount of 9.7 g/hr. Like in the case of Test Example4-2, this is attributable mainly to the fact that a part of ammonia waslost into a draft together with a non-condensable gas, and it wasevaporated during the sampling or during the preparation of the standardsolution for the analysis. The reason for the substantial difference inthe amount of potassium is not clear.

When it is considered that ammonium acetate and acetamide remaining inthe bottom (withdrawn from the column bottom) were not decomposed anddistilled, it is apparent that 75.4% of ammonia supplied as ammoniumacetate was distilled off or separated as a non-condensable gas, and atthe same time, it was possible to obtain acetic acid having anunbelievably low water content and aqueous ammonia containing no aceticacid by a distillation column having only 20 plates.

Test Example 4-4

Using the test apparatus as shown in FIG. 6, a test was carried out inthe same manner as in Test Example 4-2 except that as the feed material,ammonium acetate and potassium acetate were used, and the amount of thecharge of the feed material and the operation conditions were changed.

The charge was 250.1 g of ammonium acetate, 150.1 g of potassium acetateand 160.0 g of deionized water, and it was preheated to 90° C. To thecolumn bottom flask, for startup, 30.1 g of ammonium acetate, 20.1 g ofpotassium acetate and 70.0 g of acetic acid were charged.

When the internal temperature of the column bottom flask became 138.4°C., the feed material was supplied from the column top at a flow rate of174 cc/hr. At that time, the temperature of the preheater was 109.5° C.

After an operation for 22 minutes from the initiation of the supply ofthe feed material, 19.1 g of the distillate and 95.0 g of the bottom inthe flask were taken out as the first withdrawal. After an operation forfurther 37 minutes, 32.0 g of the distillate and 90.4 g of the bottom inthe flask were taken out as the second withdrawal.

Thereafter, a steady state was assumed.

Further, after an operation for 35 minutes, 22.8 g of the distillate and74.6 g of the bottom in the flask were taken out as the first analyticalsamples. After an operation for further 34 minutes, 28.4 g of thedistillate and 77.7 g of the bottom in the flask were taken out as thesecond analytical samples.

The compositions of the respective analytical samples were as shown inTable 4-5.

TABLE 4-5 Composition (wt %) Analytical Acetic samples acid AmmoniaAcetamide K Water First Distillate 1.3 5.8 0.0 93.0 (22.8 g) Bottom 68.52.6 4.2 16.6 8.1 (74.6 g) Second Distillate 1.1 7.5 0.0 91.4 (28.4 g)Bottom 68.8 2.2 3.2 18.6 7.1 (77.7 g)

As is apparent from Table 4-5, there is no substantial difference in thecomposition between the first and second analytical samples, and theoperation can be regarded as substantially steady. On the basis that theoperation was substantially in a steady state, if the composition of thesupplied feed material and the composition of the second analyticalsamples are compared, the mass balance will be as shown in the followingTable 4-6. Here, the supplied material of 174 cc/hr was converted to aunit of g/hr by using the specific gravity of the feed material being1.18.

Further, the amount of the acetamidated ammonia was obtained bycalculation as follows. Namely, as shown in Table 4-5, acetamide in thebottom was 2.2 wt %, which was calculated as ammonia by molar amount,which was converted to a weight to obtain 0.72 g.

TABLE 4-6 Distillate Bottom (excluding (withdrawn non- from the Suppliedcondensed column amount gas) bottom) Acetamidated Components (g/hr)(g/hr) (g/hr) ammonia Acetic 59.4 0.32 53.5 acid Water 33.1 25.9 5.5Ammonia 11.4 2.1 1.7 0.72 K 9.2 0.0 14.4

As is apparent from Table 4-6, the total of the analytical values ofammonia is 4.5 g/hr (=2.1+1.7+0.7), which is substantially differentfrom the supplied amount of 11.4 g/hr. Like in Test Example 4-2, this isattributable mainly to the fact that a part of ammonia was lost into adraft together with a non-condensable gas, and it was evaporated duringthe sampling or during the preparation of the standard solution for theanalysis. The reason for the large difference in the amount of potassiumis unclear.

When it is considered that ammonium acetate and acetamide remaining inthe bottom (withdrawn from the column bottom) were not decomposed anddistilled, it is apparent that 78.7% of ammonia supplied as ammoniumacetate, was distilled off or separated as a non-condensable gas, and atthe same time, it was possible to obtain acetic acid having anunbelievably low water content and aqueous ammonia containing no aceticacid by a distillation column having only 20 plates.

Test Example 4-5

Using the test apparatus as shown in FIG. 6, a test was carried out inthe same manner as in Test Example 4-2 except that as the feed material,ammonium acetate and potassium acetate were used, and the amount of thecharge of the feed material and the operation conditions were changed.

The charge was 250.1 g of ammonium acetate, 150.1 g of potassium acetateand 150.0 g of deionized water, and it was preheated to 90° C. In thecolumn bottom flask, for startup, 30.1 g of ammonium acetate, 20.0 g ofpotassium acetate and 70.1 g of acetic acid were charged.

Upon expiration of 21 minutes from the initiation of the temperatureraising, the feed material was supplied from the column top at a flowrate of 160.0 cc/hr. 11 Minutes later, the first distillate wasobtained, and the internal temperature of the column bottom flask atthat time was 137.2° C., and the temperature of the preheater was 108.5°C.

After an operation for 19 minutes from the initiation of the supply ofthe feed material, 10.7 g of the distillate and 102.8 g of the bottom inthe flask were taken out as the first withdrawal. After an operation forfurther 30 minutes, 31.1 g of the distillate and 79.8 g of the bottom inthe flask were taken out as the second withdrawal.

Thereafter, a steady state was assumed.

Further, after an operation for 37 minutes, 31.8 g of the distillate and76.9 g of the bottom in the flask were taken out as the first analyticalsamples. After an operation for further 38 minutes, 31.1 g of thedistillate and 79.4 g of the bottom in the flask were taken out as thesecond analytical samples.

The compositions of the respective analytical samples were as shown inTable 4-7.

TABLE 4-7 Composition (wt %) Analytical Acetic samples acid AmmoniaAcetamide K Water First Distillate 1.2 9.3 0.0 89.5 (31.8 g) Bottom 70.03.2 4.8 16.0 6.0 (76.9 g) Second Distillate 1.1 8.3 0.0 90.6 (31.1 g)Bottom 69.2 2.7 4.6 17.5 6.0 (79.4 g)

As is apparent from Table 4-7, there is no substantial difference in thecomposition between the first and second analytical samples, and theoperation can be regarded as substantially steady. On the basis that theoperation was substantially in a steady state, if the composition of thesupplied feed material and the composition of the second analyticalsamples are compared, the mass balance will be as shown in the followingTable 4-8. Here, the supplied feed material of 160.0 cc/hr was convertedto a unit of g/hr by using the specific gravity of the feed materialbeing 1.20.

Further, the amount of the acetamidated ammonia was obtained bycalculation as follows. Namely, as shown in Table 4-7, acetamide in thebottom was 2.2 wt %, which was calculated as ammonia by molar amount,which was converted to a weight to obtain 1.05 g.

TABLE 4-8 Distillate Bottom (excluding (withdrawn non- from the Suppliedcondensed column amount gas) bottom) Acetamidated Components (g/hr)(g/hr) (g/hr) ammonia Acetic 61.0 0.35 55.0 acid Water 31.9 28.2 4.7Ammonia 11.7 2.6 2.1 1.05 K 9.3 0.0 13.9

As is apparent from Table 4-8, the total of the analytical values ofammonia is 5.6 g/hr (=2.6+2.1+1.1), which is substantially differentfrom the supplied amount of 11.7 g/hr. Like in the case of Test Example4-2, this is attributable mainly to the fact that a part of ammonia waslost into a draft together with a non-condensable gas, and it wasevaporated during the sampling or during the preparation of the standardsolution for the analysis. The reason for the large difference in theamount of potassium is unclear.

When it is considered that ammonium acetate and acetamide remaining inthe bottom (withdrawn from the column bottom) were not decomposed anddistilled, it is apparent that 72.8% of ammonia supplied as ammoniumacetate was distilled off or separated as a non-condensable gas, and atthe same time, it was possible to obtain acetic acid having anunbelievably low water content and aqueous ammonia containing no aceticacid by a distillation column having only 20 plates.

Comparative Test Example 4-1

15.23 g (0.198 mol) of ammonium acetate, 15.21 g (0.185 mol) of sodiumacetate, 5.02 g (0.051 mol) of potassium acetate and 50.01 g ofdeionized water, were put into a 200 ml flask and installed in a simpledistillation apparatus. This was immersed in an oil bath heated to 180°C. When the liquid temperature in the flask became 180° C., distillationstarted. When the liquid temperature in the flask became 150° C.,heating was stopped, and the distillate and the bottom were sampled. Thedistillation time was 63 minutes. The amount of the distillate was 53.18g, and the amount of the bottom was 30.28 g. Precipitation started inabout 30 minute from the first distillation, whereby it was impossibleto measure the pH.

Acetic acid contained in the distillate was 5.47 wt % (0.049 mol), andammonia was 2.98 wt % (0.093 mol). Acetic acid contained in the bottomwas 79.32 wt % (0.400 mol), and ammonia was 0.64 wt %.

If acetic acid present in the form of an alkali metal salt (0.236 mol;from the charged amount) is excluded, it will be 0.164 mol, whichindicates that acetic acid in an amount of 24.7% of the ammonium acetate(0.198 mol; from the charged amount) which should be decomposed, wasdistilled off. A part of ammonia was discharged without being condensed,which is the reason for the unbalance.

Comparative Test Example 4-2

15.22 g (0.198 mol) of ammonium acetate, 10.00 g (0.102 mol) ofpotassium acetate and 50.05 g of deionized water were put into a 200 mlflask and installed in a simple distillation apparatus. This wasimmersed in an oil bath heated to 180° C. When the liquid temperature inthe flask became 106° C., distillation started. When the liquidtemperature in the flask became 150° C., heating was stopped, and thedistillate and the bottom were sampled. The distillation time was 51minutes. The amount of the distillate was 53.19 g, and the amount of thebottom was 20.26 g. Precipitation started immediately after thesampling, whereby it was impossible to measure the pH.

Acetic acid contained in the distillate was 5.05 wt % (0.045 mol), andammonia was 3.22 wt % (0.101 mol). Acetic acid contained in the bottomwas 76.51 wt % (0.258 mol), and ammonia was not detected.

If acetic acid present in the form of an alkali metal salt (0.102 mol;from the charged amount) is excluded, it will be 0.156 mol, whichindicates that acetic acid in an amount of 22.7% of the ammonium acetate(0.198 mol; from the charged amount) which should be decomposed, wasdistilled. A part of ammonia was discharged without being condensed,which is the reason for the unbalance.

Comparative Test Example 4-3

15.20 g (0.197 mol) of ammonium acetate, 5.00 g (0.061 mol) of sodiumacetate, 15.00 g (0.153 mol) of potassium acetate and 50.04 g ofdeionized water, were put into a 200 ml flask and installed in a simpledistillation apparatus. This was immersed in an oil bath heated to 180°C. When the liquid temperature in the flask became 108° C., distillationstarted. When the liquid temperature in the flask became 150° C.,heating was stopped, and the distillate and the bottom were sampled. Thedistillation time was 41 minutes. The amount of the distillate was 52.32g, and the amount of the bottom was 31.32 g. Precipitation startedimmediately after the sampling, whereby it was impossible to measure thepH.

Acetic acid contained in the distillate was 5.72 wt % (0.050 mol), andammonia was 3.68 wt % (0.113 mol). Acetic acid contained in the bottomwas 72.21 wt % (0.377 mol), and ammonia was not detected.

If acetic acid present in the form of an alkali metal salt (0.214 mol;from the charged amount) is excluded, it will be 0.163 mol, whichindicates that acetic acid in an amount of 25.4% of the ammonium acetate(0.197 mol; from the charged amount) which should be decomposed, wasdistilled. A part of ammonia was discharged without being condensed,which is the reason for the unbalance.

Comparative Test Example 4-4

15.20 g (0.197 mol) of ammonium acetate, 10.02 g (0.102 mol) ofpotassium acetate and 15.27 g of deionized water were put into a 200 mlflask and installed in a simple distillation apparatus. This wasimmersed in an oil bath heated to 180° C. When the liquid temperature inthe flask became 116° C., distillation started. When the liquidtemperature in the flask became 150° C., heating was stopped, and thedistillate and the bottom were sampled. The distillation time was 23minutes. The amount of the distillate was 16.65 g, and the amount of thebottom was 21.76 g. Precipitation started immediately after thesampling, whereby it was impossible to measure the pH.

Acetic acid contained in the distillate was 8.43 wt % (0.023 mol), andammonia was 7.00 wt % (0.069 mol). Acetic acid contained in the bottomwas 75.62 wt % (0.274 mol), and ammonia was 2.13 wt % (0.027 mol).

If acetic acid present in the form of an alkali metal salt (0.102 mol;from the charged amount) is excluded, it will be 0.172 mol, whichindicates that acetic acid in an amount of 11.7% of the ammonium acetate(0.197 mol; from the charged amount) which should be decomposed, wasdistilled. A part of ammonia was discharged without being condensed,which is the reason for the unbalance.

Comparative Test Example 4-5

15.20 g (0.197 mol) of ammonium acetate, 10.01 g (0.122 mol) ofpotassium acetate and 15.19 g of deionized water were put into a 200 mlflask and installed in a simple distillation apparatus. This wasimmersed in an oil bath heated to 180° C. When the liquid temperature inthe flask became 116° C., distillation started. When the liquidtemperature in the flask became 135° C., precipitation of solid wasobserved. When the liquid temperature in the flask became 150° C.,heating was stopped, and the distillate and the bottom were sampled. Thedistillation time was 23 minutes. The amount of the distillate was 17.17g, and the amount of the bottom was 21.25 g. Precipitation started,whereby it was impossible to measure the pH.

Acetic acid contained in the distillate was 11.33 wt % (0.0.32 mol), andammonia was 6.02 wt % (0.061 mol). Acetic acid contained in the bottomwas 83.97 wt % (0.297 mol), and ammonia was 2.13 wt % (0.027 mol).

If acetic acid present in the form of an alkali metal salt (0.122 mol;from the charged amount) is excluded, it will be 0.175 mol, whichindicates that acetic acid in an amount of 16.2% of the ammonium acetate(0.197 mol; from the charged amount) which should be decomposed, wasdistilled. A part of ammonia was discharged without being condensed,which is the reason for the unbalance.

INDUSTRIAL APPLICABILITY

According to the present invention, as is unexpected from theconventional acid/base reaction, it is possible to obtain free organicacid A in solid form, from an ammonium salt of organic acid A having ahigh melting point, such as a dicarboxylic acid, a tricarboxylic acid oran amino acid, produced by bioconversion of a biogenic carbon source, byreactive precipitation utilizing an acid/base reaction employing weakacid B such as a monocarboxylic acid which is a weaker acid than theorganic acid A.

Further, it is possible to recover organic acid A and its ammonium saltby vaporizing and efficiently separating acid B such as a monocarboxylicacid and an ammonium salt of acid B such as an ammonium salt of amonocarboxylic acid, from the crystallization mother liquor afterprecipitating and separating organic acid A by reactive crystallization.It is possible to increase the efficiency for separation and recovery ofthe respective substances by preventing side reactions in thisvaporization operation. It is possible to recycle and reuse theseparated acid B, organic acid A and its ammonium salt, withoutrequiring a cumbersome operation.

Further, a method is presented wherein the separated ammonium salt ofacid B such as an ammonium salt of a monocarboxylic acid, is decomposedinto acid B such as a monocarboxylic acid and ammonia by means of analkali metal or alkaline earth metal salt. At that time, it is possibleto readily separate water present in the reaction system and acid B suchas a monocarboxylic acid and to efficiently recover acid B having a lowwater content and aqueous ammonia containing no such acid.

The entire disclosures of Japanese Patent Application No. 2002-135656filed on May 10, 2002, Japanese Patent Application No. 2002-231740 filedon Aug. 8, 2002, Japanese Patent Application No. 2002-231741 filed onAug. 8, 2002 and Japanese Patent Application No. 2002-305989 filed onOct. 21, 2002 including specifications, claims, drawings and summariesare incorporated herein by reference in their entireties.

1. In a process for separating and recovering an acid B and ammonia bydecomposing an ammonium salt of acid B to the acid B and ammonia, amethod for decomposing the ammonium salt of acid B, wherein said methodcomprises: heating a liquid comprising water, the ammonium salt of acidB, and a metal salt of acid B, by supplying the liquid to a site of adistillation column having at least two plates as the real number ofplates to produce a gas of a basic aqueous solution and a remainingliquid, wherein the temperature of the site of the distillation columnis not higher than the melting point of the ammonium salt of acid B, andwherein the metal of the metal salt of acid B is one or more metalsselected from the group consisting of Na, K, Ca and Mg; and withdrawingthe gas of the basic aqueous solution from the top of the distillationcolumn.
 2. The method according to claim 1, wherein the acid B is atleast one acid selected from the group consisting of formic acid, aceticacid, propionic acid and butyric acid.
 3. The method according to claim1, wherein said method further comprises recovering the acid B bysubjecting the remaining liquid, after said withdrawing, to atemperature of at least 125° C. under reduced pressure or atmosphericpressure, and separating the acid B from a residual liquid.
 4. Themethod according to claim 3, wherein said method further comprisesmixing the residual liquid, after said separating, with an aqueoussystem to hydrolyze an amide compound formed as a byproduct in saidheating and said separating; and recycling the residual liquid, aftersaid mixing, to said heating.
 5. The method according to claim 1,wherein said method further comprises withdrawing the gas of the basicaqueous solution from the remaining liquid.
 6. The method according toclaim 1, wherein said method further comprises subjecting the gas of thebasic aqueous solution, either directly or after condensation, to a gasseparation carried out at a temperature of not higher than the meltingpoint of the ammonium salt of acid B, wherein said gas separation isselected from the group consisting of a gas/liquid separation, agas/solid separation and a gas/liquid/solid separation.